Motor too low?

[Scott79]

Just wondering what peoples opinions are, am I a hole or 2 too low? Haven't really thought too much about it previously, but the cav plate seems a fair way under, although in saying that, the water above it is quite aerated, could it just be a consequence of the hull shape? Have never experienced any cavitation of any sort in any conditions at any trim, could this be another indicator?
Boat is a Baysport, with the Concave Planing Plank - which may change things a bit?

Thanks,
Scott.

[up the creek]

im not sure if that concave planing plank will make it go ok.. and hopefully some1 who knows more then me replies... but all i know and have always been told is the concave plate on the motor should be level with the bottom of the hull.. your motor is that powerfull its going to aerate the water around it give or take a few cms .. my opinion (not professional is) the concave plate should be level...

[scottar]

The AV plate on my rig (Seafarer Victory) would be about 50mm above the vee in the hull and in reality could probably go higher but it is mounted as high as it will go. If you were to go by what seems to be the accepted standard for a vee hull, it does look too low - how that translates to a Baysport though I couldn't tell you. It's a pretty easy process to raise the engine using the jockey wheel on the trailer - costs nothing apart from some time and a tube of sealant. Just make sure you keep a good eye on either a temp gauge or better still water pressure if you do lift it to make sure you aren't doing anything nasty to your engine

[Moonlighter]

Your motor looks too deep. You are approaching this the right way, by getting the boat up to a decent cruise speed, trimmed out nicely, and then looking to see where the AV plate is in relation to the water surface. The AV plate should be skimming the surface in that picture, visible, being splashed is OK, But not buried deep under water.

That is the correct way to set engine height.

So, lift it, and then test again.

BTW that is not my opinion, it is the advice of experts around the world.

When we are helping new members of our fishing club with this issue, we put red sticky dots onto the top of the trailing end of the AV plate so its easier to see when we look at it like in your pic.

Forget about the "line it up with the hull" stuff, that is not the way to determine correct engine height. At best, it might give you a rough starting point.

[Chimo]

It looks way too low to me too.
If it were mine I would lift it at least a couple of holes and then re test. I aim to be able to get a flat hand resting on top of the water surface and below the plate when the motor is trimmed up and back at a fast cruise on good water.

Its a good thing you cannot actually test this with your hand while underway as you just might chop a few fingers!

[tunaticer]

Before you go making big jumps in raising the motor, see how it handles first.
Some hulls can be bitches making the prop cavitate whilst cornering.
Last thing you want is to have a motor that breaks out when cornering.

It does look low, but would depend on how the concave planing plank operates on a high speed corner, it may introduce air to the prop.

[Chimo]

I guess we should also ask what prop is on the motor?. Some like it deep some not.
And how does it corner?
Does the prop break out on tight corners?

If it does not break out on corners with skiing type turns then raising the motor answers the question does it look too low, is it too low

[Spaniard_King]

Your motor looks too deep. You are approaching this the right way, by getting the boat up to a decent cruise speed, trimmed out nicely, and then looking to see where the AV plate is in relation to the water surface. The AV plate should be skimming the surface in that picture, visible, being splashed is OK, But not buried deep under water.

That is the correct way to set engine height.

So, lift it, and then test again.

BTW that is not my opinion, it is the advice of experts around the world.

When we are helping new members of our fishing club with this issue, we put red sticky dots onto the top of the trailing end of the AV plate so its easier to see when we look at it like in your pic.

Forget about the "line it up with the hull" stuff, that is not the way to determine correct engine height. At best, it might give you a rough starting point.

The above advice is far from true!!

If the cav plate does skim the surface then the ride quality of the boat will suffer. Most offshore boats will handle better if there is some level of water flowing over the cav plate at neutral trim( I like at least 1/2") By doing this you have more chance of the boat handling better in rougher conditions and you will need less negative trim to hold the nose into chop.

Yes you will loose a tiny bit of top end but do you drive around at WOT all day !!!

[Scott79]

Thanks guys, some good input. At best guess, after taking some measurements off the motor and looking at a couple of other pics I took, water level is ~50mm above the cav plate at the furtherest point, so I am leaning towards lifting it one hole to try. Boat handles fine as it is, no sign of cavitation through tight turns etc. If anything though, I would probably like to be able to trim the nose down a bit further when running a very light load - not sure if that is related though?

Spaniard King, any idea how much top end speed and RPM would suffer from being a little too deep, no doubt there are countless variables, but would it be likely to be 4-5km/hr and a couple of hundred RPM worst case???

Moonlighter, I like the idea of the red dots for better visibility of the cav plate, makes sense.

Thanks to all.
Scott.

[Chimo]

Scott

After reading "I would probably like to be able to trim the nose down a bit further when running a very light load" one wonders if you have trim tabs on the boat?

If fitted these would certainly allow you to trim the nose down and also allow you to keep the boat level so the bow works as it was intended to give a smoother ride in choppy conditions.

Plate tabs such as Lenco or Bennett will also assist getting up on the plane and holding plane at a slower speed and this is even without lowering them so drag is minimized.

Plate trim tabs also, from experience with the weight of two motors on the transom allow quicker planing even without tucking the motors all the way in to the transom which certainly assisted planing before the tabs (Lenco 9 x 9 ) were fitted.

What prop are you using?

Cheers
Chimo

[gofishin]

... At best guess, after taking some measurements off the motor and looking at a couple of other pics I took, water level is ~50mm above the cav plate...If this is indeed the case, your motor is way too low.

However, the concave planing plank will definitely complicate comparison(s) to a 'more normal' hull.

By definition/shape trait, the concave surface will entrain and in fact concentrate any air/vapour along the centreline, directly in front of the outboard/prop.

So... my 2c... best to raise one hole at a time, then when you get too high - whatever that is - you will know and can drop back down, knowing how it performed at the previous hight. More tedious, yes, but will provide the best result 'in the end'.


... If anything though, I would probably like to be able to trim the nose down a bit further when running a very light load - not sure if that is related though? ....Not sure why you stated/highlighted a light load scenario, but raising the motor will level the attitude/stance of the boat,i.e. drop the bow - without changing the motor trim. This is pure physics. In other words, your bow will drop without tucking the motor in.
Cheers
Brendon

[scottar]

So... my 2c... best to raise one hole at a time, then when you get too high - whatever that is - you will know and can drop back down, knowing how it performed at the previous hight. More tedious, yes, but will provide the best result 'in the end'.



I agree 100%. I have completed this procedure about half a dozen times on my rig - first few times with the original prop as supplied which in the end didn't like the highest position (lost a few knots at WOT) so had to come down a hole and then again when I started swapping to props with more blade area that are happy to run higher. Using an air socket wrench (soon becomes your new best friend doing this job for winding the bolts out of the transom), and two people, once you wrap your head around the procedure it only takes about half an hour.

Also agree with Chimo - if your running bow high due to weight distribution when lightly loaded - get a set of trim tabs fitted. Turns the rig into a different boat

[Moonlighter]

If this is indeed the case, your motor is way too low.

Not sure why you stated/highlighted a light load scenario, but raising the motor will level the attitude/stance of the boat,i.e. drop the bow - without changing the motor trim. This is pure physics. In other words, your bow will drop without tucking the motor in.
Cheers
Brendon

Agree 100% with Brendon. Never argue with an engineer! Youll get a lesson about angles of thrust and the like before you can blink!

Definitely see a more level attitude of the boat when motor height is optimised to a higher position than when it is buried too deep. I think you will find that your boat runs flatter when light as well as loaded after you lift it. A boat with a more level basic "attitude" will run better in all conditions, inshore or offshore, and the boat responds better to trim changes as well. I've seen boats with engines that were buried transformed from dogs to sports cars when the engine height has been optimised.

As Chimo noted, once you get into the right engine height "zone", this is where the characteristics of your chosen prop plays a significant role. Some provide greater stern lift, others less so. Some lose grip more easily, others hang on just fine. Standard alloy props tend to not grip as well as a good stainless prop or even an average stainless prop, so those more ordinary props may need the engine to be dropped lower to perform at their best.

[Scott79]

Not sure why you stated/highlighted a light load scenario, but raising the motor will level the attitude/stance of the boat,i.e. drop the bow - without changing the motor trim. This is pure physics. In other words, your bow will drop without tucking the motor in.
Cheers
Brendon

That's exactly why I have mentioned it - to get the answer you have just given me!
Hopefully by coming up a hole it may provide a wider/different trim range so I can get the bow down a bit further when travelling light. It isn't bad enough to be a necessity, but it will be a welcome benefit all the same.

Hadn't really thought about fitting trim tabs as a few people had mentioned, not saying it wouldn't benefit from tabs, but I don't really see the need as it is easy enough to distribute weight sensibly most of the time. Last boat I had was a plate boat that leaned into the wind badly, I think if it had that characteristic I would probably go down the path of tabs.

Scott.

[Scott79]

If this is indeed the case, your motor is way too low.

However, the concave planing plank will definitely complicate comparison(s) to a 'more normal' hull.

By definition/shape trait, the concave surface will entrain and in fact concentrate any air/vapour along the centreline, directly in front of the outboard/prop.
Brendon

This is the part that confuses me - I am not sure how much of the water above the cav plate is a consequence of the hull shape, it definitely looks very aerated.

[fisho64]

Spaniard King, any idea how much top end speed and RPM would suffer from being a little too deep, no doubt there are countless variables, but would it be likely to be 4-5km/hr and a couple of hundred RPM worst case???

.
It does make a difference, but maybe not as much as you'd expect, in a fishing boat at least.
My boat has twin Suzi's 25", and when I got it I quickly realized it was WAY too low, like 6" as there was spray everywhere around the stern.
Appeared that whoever set it up thought that because it needed a 25" single, it also needed 25" twins.
It was also on the lowest hole.
I raised them to the highest hole (up about 100mm from memory) and maybe gained about 3 knots tops and a few hundred rpm, but it is lighter on the wheel.

[Scott79]

It does make a difference, but maybe not as much as you'd expect, in a fishing boat at least.
My boat has twin Suzi's 25", and when I got it I quickly realized it was WAY too low, like 6" as there was spray everywhere around the stern.
Appeared that whoever set it up thought that because it needed a 25" single, it also needed 25" twins.
It was also on the lowest hole.
I raised them to the highest hole (up about 100mm from memory) and maybe gained about 3 knots tops and a few hundred rpm, but it is lighter on the wheel.

Cheers mate, thanks.

[scottar]

Hadn't really thought about fitting trim tabs as a few people had mentioned, not saying it wouldn't benefit from tabs, but I don't really see the need as it is easy enough to distribute weight sensibly most of the time.

Scott.

Spoken like a man that has never had tabs before. Not being derogatory - I used to say exactly the same thing. Now having put them on my own boat and having seen the difference they make to the ride and capabilities, I have exactly the opposite opinion. If you have never had them you seriously don't know what you are missing - I know I didn't.

[Chimo]

Listen to Scottar.............and heed his advice.

[Scott79]

Spoken like a man that has never had tabs before. Not being derogatory - I used to say exactly the same thing. Now having put them on my own boat and having seen the difference they make to the ride and capabilities, I have exactly the opposite opinion. If you have never had them you seriously don't know what you are missing - I know I didn't.

I expected this response mate! I did investigate tabs a bit when I had the previous boat, but in the end couldn't justify it as I wasn't really using it much, but alot of comments of the same nature - "every offshore boat should have them" etc etc.
Not suggesting they aren't worthwhile, but to be honest they aren't really on the cards at the moment though. I think if this one had the lean that the last boat had it would be a different story.

[Dignity]

I expected this response mate! I did investigate tabs a bit when I had the previous boat, but in the end couldn't justify it as I wasn't really using it much, but alot of comments of the same nature - "every offshore boat should have them" etc etc.
Not suggesting they aren't worthwhile, but to be honest they aren't really on the cards at the moment though. I think if this one had the lean that the last boat had it would be a different story.
I installed trim tabs on my boat when I got a new motor, it was the best thing I ever did and I had never previously had them or experienced them, for fairweather boaties may not experience a lean but there are times when wind will make it do so but from my limited experience I use the trim tabs mostly to adjust the trim of the boat before adjusting the trim on the motor and found that I could not go back to not having them and it would also go most of the way to solving your bow lift problems. My boating (in this particular boat as I also have a tinnie which gets 200 hrs ayear) is limited to around 80 hrs a year unlike some of those giving you advice such as Scottar, Moonlighter, Chimo, Spaniard King and the others. In essence imho wind lean is not the main reason for trim tabs and for a grand or less you would wonder how you did without them. Saying all that it was a learning experience to use them and you still should be trimming your motor out for optimum performance.
There is one guy I sometimes go out with who won't trim his motor at all once in the water, some very interesting rides and I can't convince him to try.

[gofishin]

On holidays with too much time on my hands this week, have you noticed...??? [emoji15]

Been scrolling thru posts in recent threads that I originally skipped/skimmed over ...

The above advice is far from true!!

If the cav plate does skim the surface then the ride quality of the boat will suffer. Most offshore boats will handle better if there is some level of water flowing over the cav plate at neutral trim( I like at least 1/2") By doing this you have more chance of the boat handling better in rougher conditions and you will need less negative trim to hold the nose into chop...I disagree about the "this is far from true" Garry.

For some boats, yes they certainly 'handle' better with the AV plate buried a little, and some props (or 'props and outboards') do like/need the plate to be buried a little (regardless if the boat needs this or not).

Not having a go at all mate, but I think we also need to separate 'handling' (ride quality, ease of planing, on-plane nimbleness, and low-speed planing ability etc etc); from 'ventilation' issues. As you would know, motor height affects handling regardless if ventilation is experienced or not.

Oh, and I don't want a black mark on my name whenever my little Honda needs to be looked after... or if I ever want a big Honda ... [emoji6]. Just thought I would raise debate on a few related issues. [emoji1]

I think there are always a few factors at play; boat, prop, outboard make, and a combination of all three; whether there is a pod involved, and what type; and probably even the skipper too I guess (preferences may differ)!

Obviously the prop does play a big part in that some are a lot more happier running higher than others, and some boats even need high mounted props to handle/perform the best.

For instance, my boat's handling loves the plate at or even above the surface - currently ~50 something above the keel plank. Finding a prop to accommodate this and provide great performance was tedious, and over the years I tried maybe 10 or so on my boat, let alone many more on mates boats with different setups (that wouldn't suit my boat, else I would have tried them too).

In reality, with the current prop the donk on my boat is probably a third to possibly a 1/2 hole too high - because it suffers a bit of ventilation in very tight turns in real snotty conditions - like when you run over a lump at speed and want to do a quick grid pattern (while still at speed), with 20knots of wind.

However, the boat handles so much better at this position than one hole down, and since I don't want to fill transom holes and re-drill the transom, it is staying there. (and I do have a plan, just need to find a particular prop - at the right price - and get it tuned & repitched by adding some extra cup).

However, if my boat had a stepped/clearwater pod, this current engine height would be useless.

The 4 blade Powertech ELE I bought off you years ago (and sold back to you a few yrs later [emoji1] ) was a good allrounder, but ventilated terribly in tight turns on my boat, and couldn't be run above neutral trim at the original engine height. Otherwise good transom lift and ok handling. A good 'height' to run this prop to eliminate all ventilation would be 2 holes below where the donk currently is at! BUT, the extra nose up generated by a lower prop (even if it is a 4 bld with good transom lift) would have made the handling suffer a little.

However, this exact prop on a mates similar but slightly smaller boat, with a different brand & smaller HP OB, stuck like sh!t to a blanket, even with tight turns - and at the highest mounting position possible, with the plate ~60 above the plank from memory. Go figure!

Another mate, after a lot of research and advice from Ken @ prop gods, imported a Powertech OFS4/OFX4 ?? from them, supposedly the PT premier 4 blade prop for offshore boats. This thing on a 685 and F300 needed the donk one hole lower than even for a yammy 3 bld SS2 T series prop, else it would spit the dummy on occasion and grab 3-400 revs and spin air, speed would drop considerably and in this case handling was affected if it dropped off the plane.

Wouldn't even come close to the performance and boat handling of a REV 4 on the same boat, yet on US boats the performance between the 2 prop types is reversed at times, and with high mounted engines too. WT? Obviously different boats, and maybe the yank boats don't have keel planks??

Zukes 300's are an ever increasingly popular repower option in the US, mostly for their previously much loved yammy's 225-300's (and E-TEC's), yet on average they need to be mounted one hole lower, keeping the plate lower/slightly buried & not skimming like their old donks were (whatever brand). Why? Gearcase design? Slow prop speed (ratio)? Big diam props? Always thought this was because they run larger diam props, but apparently not as guys trying same diam props as they previously used could still not solve their issues other than dropping a hole and going back to Zuke props.

Right or wrong, a common fix to correct a pressed tinny that was mistakenly made with a flat or even hogged hull (i.e. that ploughs/tends to broach) - which couldn't be corrected by hull reshaping - is to burry the donk 1 or 2 holes below 'normal' to generate additional bow lift. Personally, I always like to 'fix the fault' rather than just 'fix the problem'. Bandaids are for cuts!

I guess it also comes back to the skipper's preference too. I have been on some boats where I have felt that the handling would benefit from lifting the motor, but have also been on some where I would be dropping the motor, just for handling benefits. The owners don't always care/feel the same though [emoji1].

Damn, that was a lot of thumb taps on the phone!

Cheers
Brendon

[gofishin]

... Boat is a Baysport, with the Concave Planing Plank - which may change things a bit?...Just looked closely at your transom pick Scott, and actually you have a 'keel plank' not a planing plank. There is a difference, and the former does create more ventilation issues during turns. Yours being concave just complicates it further.

[Spaniard_King]

On holidays with too much time on my hands this week, have you noticed...??? [emoji15]

Been scrolling thru posts in recent threads that I originally skipped/skimmed over ...
I disagree about the "this is far from true" Garry.

For some boats, yes they certainly 'handle' better with the AV plate buried a little, and some props (or 'props and outboards') do like/need the plate to be buried a little (regardless if the boat needs this or not).

Not having a go at all mate, but I think we also need to separate 'handling' (ride quality, ease of planing, on-plane nimbleness, and low-speed planing ability etc etc); from 'ventilation' issues. As you would know, motor height affects handling regardless if ventilation is experienced or not.

Oh, and I don't want a black mark on my name whenever my little Honda needs to be looked after... or if I ever want a big Honda ... [emoji6]. Just thought I would raise debate on a few related issues. [emoji1]

I think there are always a few factors at play; boat, prop, outboard make, and a combination of all three; whether there is a pod involved, and what type; and probably even the skipper too I guess (preferences may differ)!

Obviously the prop does play a big part in that some are a lot more happier running higher than others, and some boats even need high mounted props to handle/perform the best.

For instance, my boat's handling loves the plate at or even above the surface - currently ~50 something above the keel plank. Finding a prop to accommodate this and provide great performance was tedious, and over the years I tried maybe 10 or so on my boat, let alone many more on mates boats with different setups (that wouldn't suit my boat, else I would have tried them too).

In reality, with the current prop the donk on my boat is probably a third to possibly a 1/2 hole too high - because it suffers a bit of ventilation in very tight turns in real snotty conditions - like when you run over a lump at speed and want to do a quick grid pattern (while still at speed), with 20knots of wind.

However, the boat handles so much better at this position than one hole down, and since I don't want to fill transom holes and re-drill the transom, it is staying there. (and I do have a plan, just need to find a particular prop - at the right price - and get it tuned & repitched by adding some extra cup).

However, if my boat had a stepped/clearwater pod, this current engine height would be useless.

The 4 blade Powertech ELE I bought off you years ago (and sold back to you a few yrs later [emoji1] ) was a good allrounder, but ventilated terribly in tight turns on my boat, and couldn't be run above neutral trim at the original engine height. Otherwise good transom lift and ok handling. A good 'height' to run this prop to eliminate all ventilation would be 2 holes below where the donk currently is at! BUT, the extra nose up generated by a lower prop (even if it is a 4 bld with good transom lift) would have made the handling suffer a little.

However, this exact prop on a mates similar but slightly smaller boat, with a different brand & smaller HP OB, stuck like sh!t to a blanket, even with tight turns - and at the highest mounting position possible, with the plate ~60 above the plank from memory. Go figure!

Another mate, after a lot of research and advice from Ken @ prop gods, imported a Powertech OFS4/OFX4 ?? from them, supposedly the PT premier 4 blade prop for offshore boats. This thing on a 685 and F300 needed the donk one hole lower than even for a yammy 3 bld SS2 T series prop, else it would spit the dummy on occasion and grab 3-400 revs and spin air, speed would drop considerably and in this case handling was affected if it dropped off the plane.

Wouldn't even come close to the performance and boat handling of a REV 4 on the same boat, yet on US boats the performance between the 2 prop types is reversed at times, and with high mounted engines too. WT? Obviously different boats, and maybe the yank boats don't have keel planks??

Zukes 300's are an ever increasingly popular repower option in the US, mostly for their previously much loved yammy's 225-300's (and E-TEC's), yet on average they need to be mounted one hole lower, keeping the plate lower/slightly buried & not skimming like their old donks were (whatever brand). Why? Gearcase design? Slow prop speed (ratio)? Big diam props? Always thought this was because they run larger diam props, but apparently not as guys trying same diam props as they previously used could still not solve their issues other than dropping a hole and going back to Zuke props.

Right or wrong, a common fix to correct a pressed tinny that was mistakenly made with a flat or even hogged hull (i.e. that ploughs/tends to broach) - which couldn't be corrected by hull reshaping - is to burry the donk 1 or 2 holes below 'normal' to generate additional bow lift. Personally, I always like to 'fix the fault' rather than just 'fix the problem'. Bandaids are for cuts!

I guess it also comes back to the skipper's preference too. I have been on some boats where I have felt that the handling would benefit from lifting the motor, but have also been on some where I would be dropping the motor, just for handling benefits. The owners don't always care/feel the same though [emoji1].

Damn, that was a lot of thumb taps on the phone!

Cheers
Brendon
Did you just not contradict yourself over and over and maybe over again :) :) :) :)

[Fed]

I think the guy (Glen?) on the Verado site is full of it & I've even seen posts where Ken? the prop God tries to distance himself from him. Just saying.
If it wasn't for the disclaimer on the 'Verado' site Mercury would have pulled his pin years ago.

[gofishin]

Did you just not contradict yourself over and over and maybe over again :) :) :) :)

Maybe! It was late! [emoji1]

Shortened version. Motor height for optimum handling not always the same as motor height to prevent ventilation.

How's that? [emoji1][emoji1]

[Scott79]

Just looked closely at your transom pick Scott, and actually you have a 'keel plank' not a planing plank. There is a difference, and the former does create more ventilation issues during turns. Yours being concave just complicates it further.

I didn't know there was a difference? Manufacturer refers to it as a Planing Plank.
Regardless, I am still pretty convinced I will try raising it a hole and see what impact it has, but it probably won't happen soon.

Scott.

[gofishin]

I didn't know there was a difference? ...All to do with how the 'flat' is created.

Think of a 'model' of a typical vee hull made of surfboard foam, and take a slice off the bottom, creating a wedge tapering down to nothing the further forward you slice (say 1/3 to 1/2 way forward). This = a planing plank.

Do the same as above, but don't start with such a wide flat at the transom, and take the wedge further forward. Then, take a thin slab of foam, same shape as the wedge you just sliced off the hull, and glue it to the bottom of the hull.
This = a keel plank (which have shoulders either side of the flat), & these shoulders also work like a keel (albeit a small keel).

Look at your transom pic either side of your bungs, see the shoulders?

There are pros & cons for each type.

Examples that come to mind:

Haines Sig VDH series = planing plank.

Current Cruise Crafts, and the old Haines 773 model (for one) = keel plank.

Yes, raise one hole and see how it goes.
Cheers