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seastorm
27-12-2009, 07:15 PM
I took the boat out today (6.1m Plate boat with a 150 Etec on the back) as it has been August since its last run and will be using it a bit in the next few weeks.

I remember a post on here a few months ago talking about motor height prop size and WOT.

Today was the day to check this out and I think my setup is all wrong?

WOT 4900 - 5000rpm, and 30mph if I tilt the motor up till just before it cav's I get another 5mph out of it the the rev's stay the same

I tried to look at the skim plate but water was everywhere, I think due to the bait tank and deck wash pick ups.
I feel that the oil and fuel figure's are a bit sad as well,.

Here is a few photo which in the right eye's might make sense

robothefisho
27-12-2009, 09:36 PM
By the looks of it the bottom of that pipe is running above the cav plate? This and the figures you provided suggest it is probably an inch, inch and a half to low. I'd want to be seeing WOT rpm up around 5500 atleast. Just try lifting a hole and see what happens. You may find in rough water it starts ventilating too easily. Everythings a compromise. A 17 pitch prop seems right for an alloy 6m boat. If anything could probably pull a bigger pitch prop so shouldn't have any problems getting the revs up lifting the motor a hole or possibly two.

FNQCairns
27-12-2009, 09:45 PM
Yes it looks like 1 hole minimum, you may get 2 if the water you travel is not rough and of coarse personal preference, those etecs seem to be recommended in setup rpm a little strange historically speaking, with even 5300 being considered ok when the top of the range is 5500 or so...I don't believe it's anywhere near ideal but seems accepted and will still see them through warranty but i wouldnt want to buy one out side of warranty.

Oh BTW 5000rpm WOT makes for one hell of a dog of a boat, you have gotta do something about that.

cheers fnq

bigjimg
27-12-2009, 10:00 PM
I would even consider you put a wedge on the transom as well to counter that acute angle of transom to cav plate when trimmed in as well.Jim

finga
28-12-2009, 06:56 AM
In the last picture there seems to be a very faint line just above the water intake.
Is this a line, and if it is, what does it relate to?
If this is where the water is when planing then the motor definitely needs to be lower.
That line (if it is a line) needs to be just under the cav.plate.
I reckon it's hard to tell from these pictures as they are not taken square onto the side of the boat so you can see the bottom of the hull and where the lines go to.

seastorm
28-12-2009, 07:31 AM
More Photos added
When I place the 20mm conduit on top of the cav plate and run it back to the transom the height looks ok. Does the angle of the motor to the transom and bottom of the hull look ok?

finga
28-12-2009, 07:52 AM
Mate, Is that a faint line on the leg just above the water intake?

seastorm
28-12-2009, 08:04 AM
Hi Finga
Yes that is a faint line above the water intake, don't know what it is and it just wiped off

Chimo
28-12-2009, 08:31 AM
Hi Guys

Just came across the thread.

If it was mine I'd lift it minimum 2 holes and probably go 3 as its easy to drop them at the ramp during a test. Just take the trailer off the car and place a block of wood under the skeg and move the transom up and down with the jockey wheel.

You know your at the right height for fresh ie river or lake water when the motor cavitates easily on hard turns when you run the rig in sea water!

With the boat running between fast cruise and high speed with the motor trimmed up and back for optimum running the cav plate should be clear of the water surface.

Not sure if your props correct but thats another issue to resolve.

Cheers
Chimo

top_deck69
28-12-2009, 08:36 AM
hi all,

I'm also having troubles with prop size, I have a 4.8m glass boat (galeforce side console) with a 75 etec and it will only revs out to 4300rpm WOT, granted I get 35mph at this, current prop is a 13 7/8 * 17 viper. where would be the best place to take it to get assessed and a better prop suggested??

I've heard mixed reports about dealers who generally just put a mediocre prop on the motor as part of the package and out the door you go.

Seastorm, don't mean to hijack your thread just didn't want to post another with exactly the same question

Cheers
Ben

finga
28-12-2009, 08:38 AM
Hi Finga
Yes that is a faint line above the water intake, don't know what it is and it just wiped off
Goodo. Have you run it in a tank of late?
The only reason I ask is IF that line is from running in the open water then that's a line that will tell you where the motor is sitting at planing speeds.
If the line is from the motor running in a tank or bucket you need more water in the bucket.
But by looking at the new pictures it seems to need to go up a tad.

Jabba_
28-12-2009, 08:38 AM
Your motor should be raised up 1 more hole...
Once you have done that, take it for a spin with its normal load (Not a light load).. If your not getting 5500rpm with your normal load ten you will need to reduce your propeller pitch.. By how much will depend on what RPM you get after you raise your motor....

Also the SST is the bottom off the range prop. You may want to look at the Viper, Rebel or the Rogue.. Can you post up a pic off your entire boat and how much does it weighs...

Moonlighter
28-12-2009, 08:47 AM
Hi Seastorm

I've posted this info a few times before in response to similar inquiries, and it's still the best and clearest explaination I've seen about how to tell if your motor height and prop selection are correct. So in case you haven't seen it, here it is again!

Engine height has a huge impact on your boat's performance - acceleration, speed and fuel economy all impacted. In fact, you could already have the correct prop but if the engine is too low, it could be the one thing that is limiting your performance.

See this link, it really is worth a read and a look at the pics:
http://www.veradoclub.com/smf/index.php?topic=137.0 (http://www.veradoclub.com/smf/index.php?topic=137.0)

It includes excellent pictures taken when the boat is at speed to show you how a cav plate looks when its too deep and when its at the right height.

It also tells you in very precise and easy to understand terms how to determine if you have a prop fitted that suits your boat/motor.

Cheers

ML

seastorm
28-12-2009, 09:13 AM
Thanks Moonlighter
I had a look at this site before when it was posted and it is a good site, yesterday I tried to look at the cav plate when on the plane but I could not see too much as there was water going everywhere from the live bait tank and deck wash pick ups. I have now turned these pick up sideways in a hope to see what is going on at the cav plate.

Makka Nick
28-12-2009, 09:17 AM
Just my 2 cents worth...

Changing from a 19 - 17" pitch prop on my 150 Etec took me from 5200 to 5600 rpm and dramatically changed the handling of the boat for the better. If you're only getting 5000 rpm I don't think raising the engine alone will help, you might want to try a 15" pitch prop also.

You need to get the revs up to about 5400rpm at least, otherwise you're sending the motor to an early grave.

FNQCairns
28-12-2009, 10:11 AM
hi all,

I'm also having troubles with prop size, I have a 4.8m glass boat (galeforce side console) with a 75 etec and it will only revs out to 4300rpm WOT, granted I get 35mph at this, current prop is a 13 7/8 * 17 viper. where would be the best place to take it to get assessed and a better prop suggested??

I've heard mixed reports about dealers who generally just put a mediocre prop on the motor as part of the package and out the door you go.

Seastorm, don't mean to hijack your thread just didn't want to post another with exactly the same question

Cheers
Ben

I don't know your engine hardly at all but would either check the tacho output or the speedo output first to be sure of your numbers.

If they are accurate (did you mean km/h even, although that on the surface doesn't seem to work either) then assuming you keep the same diameter you need to go down 2 in pitch to test...then of coarse go finer from there.

If re-proping it's always advantageous to decrease diameter before pitch...if you can get away with it.

cheers fnq

Jabba_
28-12-2009, 10:34 AM
Seastorm... I have found that the Bar Crusher with a 150 E-tec the 15" Rebel is the best prop... On your rig it should also be a good choice... I have found the SST and Viper get a bit too much slippage with heavy boats.. The Rebel has 3 big blades and big diameter, it has heaps off bite and is much more efficent....

If I were you, once the hieght was sorted, I would be getting my hands on a 15" Rebel...

For the bay or bluewater the Rebel gives your much more control off your speed, and heaps better slow speed planing.... Top speed is only reduced 1-2mph, in some cases there is no loss at all....

seastorm
28-12-2009, 02:36 PM
Jabba
You reckon to go to a 15" Rebel what sort of pitch do you go for or are they all the same? What sort of $ are we looking at and where do I get one from?

Jabba_
28-12-2009, 05:43 PM
15" is the smallest Rebel... I use a 19", but I could go to a 21" Rebel and still be in the Optimum rev range... The only reason I don't have a 21" is strictly a financial reason, I don't have the spare cash floating around at the moment...

Your best to buy the prop from the states, it will cost you about $500 to your door.. It takes 4-5 days to get it in from the States.

In Australia it will take 2 weeks to get it and cost $900....

I think the 15" Rebel should be the ticket, but we really need to see how many rpm's you pick up first once your lift your motor... So get your engine hieght sorted first, check RPM and we can go from there......

Fed
29-12-2009, 07:48 AM
I think your motor height is fine seastorm, did you add some extra pics to your first post, I only saw 3 or 4 the other day and now I see more pics that show your height quite clearly.
You're either not making enough power or your prop is too tall.

Spaniard_King
29-12-2009, 08:21 AM
Sea Storm, What HP is that Hull rated too??

I would not be going up any more than 1 hole! As has been mentioned prop choice will give you the best performancve increase in your situation.

top_deck69
29-12-2009, 10:36 AM
Hi FNQ,

Thanks for the info, The speed is from GPS and probably actually a little on the conservative side, I can get 32-33 knots with the motor trimmed out a little, just starts to cavitate, but still only max 4300 rpm, 2 onboard with a live well full, on Brisbane river.

I can only assume that the tacho is working, standard etec anologue gauge.

I was talking to Jabba and he also suggested a 15" prop either a 3 or 4 blade. He suggested looking at getting a 4 blade evinrude Rogue (13 1/4 X 15")

Cheers
Ben



I don't know your engine hardly at all but would either check the tacho output or the speedo output first to be sure of your numbers.

If they are accurate (did you mean km/h even, although that on the surface doesn't seem to work either) then assuming you keep the same diameter you need to go down 2 in pitch to test...then of coarse go finer from there.

If re-proping it's always advantageous to decrease diameter before pitch...if you can get away with it.

cheers fnq

top_deck69
29-12-2009, 04:38 PM
Hi All

I did some test runs today to ensure that I had everything right, with a slightly lighter load than normal, 1 onboard and half a tank of fuel, still with the bait tank full (plus an amount of extra water as is was pouring rain when I was out), I managed to get the motor up to 4800-4900 rpm but this was fully trimmed up, I mean the needle on the trim gauge wouldn't go any higher, I managed 34.5 knots but felt that there was minimal control left and would not turn with the engine like this. I was getting a fair amount of prop ventilation aswell.

I noticed on a normal plane (moderate trim) that I couldn't see the cavitation plate so I'm guessing that means its underwater?? When I trim right up as above I see the plate. does this mean that the motor needs to be lifted??

With the boat on the trailer and the motor trimmed so the cav plate is parallel with the bottom of the hull the cav plate is just on 25mm above the bottom line. Motor currently in second hole from the top (four total).

I would rather get the motor height etc sorted before I fork out dollars on a new prop

Cheers
Ben


Hi FNQ,

Thanks for the info, The speed is from GPS and probably actually a little on the conservative side, I can get 32-33 knots with the motor trimmed out a little, just starts to cavitate, but still only max 4300 rpm, 2 onboard with a live well full, on Brisbane river.

I can only assume that the tacho is working, standard etec anologue gauge.

I was talking to Jabba and he also suggested a 15" prop either a 3 or 4 blade. He suggested looking at getting a 4 blade evinrude Rogue (13 1/4 X 15")

Cheers
Ben

Moonlighter
29-12-2009, 05:47 PM
Hi Ben

You've definitely got the right idea which is to sort out the engine height first before playing the prop-swap game!

See the post I put up with the link to to the Verago Club website - there you'll find very clear guidelines about how to check the height and the trim/speed etc at which you should be able to see the cav plate.

Lifting engine by a notch or 2 is pretty easy.

I lifted the 70 Yammy I had a few years ago simply by trimming the motor most of the way in, then winding the jockey wheel up until the skeg touched the ground (actually rested it on a piece of plywood). Then loosened the bolts, had one of the mates steady the motor, then undid the bolts and slid the trailer fwd carefully a few inches (brakes on!)- voila, its off!

Then wound the jockey wheel up a few turns until the motor bracket was lined up with the correct holes in the engine bracket, slid the trailer back, and with a bit of a jiggle the motor was back on. Tighten up and you're away. 30 minute job, easy. Couple of helpers make it safe and easy. Doing it this way you don't even need to disconnect the steering, but can do so if you like - if its the std cable steering its easy to disconnect.

Your 70 etec is also pretty light so similar to the Yammy.

The test again and see how it goes.

As seen from the posts on that Verado site, easy to pick up 300-400rpm or even more with the correct engine height.

Cheers

ML

MackerelMan
29-12-2009, 08:29 PM
Interesting thread. Does the general rule of having the cav plate just out of the water at plane apply to Honda's as well. From memory Honda owner manuals talks about the cav plate being at least 4 inches below water level in order to ensure cooling. There is alot of leg 4 inches above the plate being plowed thru the water at such a set up. I am guessing this is a Honda safety marging thing but ot sure.

cheers

Spaniard_King
29-12-2009, 08:45 PM
Colin,

The same rule applies for ALL engines, Honda is or should be making reference to the water intake being 100mm/4 inches below the water not the cav plate. Have never herd of the cav plate having the 4 inch requirement.

MackerelMan
29-12-2009, 08:55 PM
Thanks Garry, I thought it was sus but was not sure. Thanks for the help.

cheers

CD