Have I got the wrong outboard? RE: transom weight.

[Dirtfloor]

What have I done? :-[ I spent three years rebuilding this boat and I bought this Johnson 225 and then I read all this stuff on Ausfish about Transom weights.
The boat is 5.5 mt half cabin and the outboard came off a 5.5 mt racing boat so I figured I would be okay. I can't find anything on the net to tell me how to work out if the two are compatible. I haven't mounted the motor yet and I have to get the boat measured for a HIN. Would that give me some indication of what is the right outboard for the boat. The motor weighs 207 kg, that much I've worked out. Somebody please tell me I haven't stuffed up!!

[Chimo]

What breed is the boat?

The manufacturer specs will tell you what should be the max weight and HP.

From the sound of it tho you may have a very quick boat, not necessarily safe or insurable but certainly quick with 225 on 5.5 m.

Check the specs and if you dont have them tell us what breed the boat is and some one on here will know.

Cheers
Chimo

[Dirtfloor]

72529I don't know what breed it is but I'll try to post a photo. Maybe someone can recognise it.72528

[Chimo]

DF

Your attachment didn't show

Suggest you read this to see what the issue may be: http://www.ausfish.com.au/vforum/showthread.php?103565-Attaching-photos-files-to-posts

Cheers
Chimo

[Dirtfloor]

I'll try again72536

[deckie]

pride albatross/stejcraft maybe ?? Would help immediately if u said what she is.
Seriously, thats a LOT of hp and weight...u really need to lookup the transom specs for the make/model. 225 is likely about 100hp more than needed. You dont want to get on the gravy train of trying to change the hull to fit the donk. "Racing" or even ski boats are an entirely different thing regards HP and design. By the time you've put some fluids in that donk will be well over the 210kg, plus are the petrol tanks above floor down back or sublfoor up middle ?..more hp =more fuel to carry=more weight

[patske]

pride albatross/stejcraft maybe ?? Would help immediately if u said what she is.
Seriously, thats a LOT of hp and weight...u really need to lookup the transom specs for the make/model. 225 is likely about 100hp more than needed. You dont want to get on the gravy train of trying to change the hull to fit the donk. "Racing" or even ski boats are an entirely different thing regards HP and design. By the time you've put some fluids in that donk will be well over the 210kg, plus are the petrol tanks above floor down back or sublfoor up middle ?..more hp =more fuel to carry=more weight
I agree with deckie - sure will be a rocket though.
Have yoU thought about how much fuel you will need for your trips???
Probably not the most economical motor for a 5.5m vessel.

[Dirtfloor]

I've found an identical boat for sale on eBay. The seller says it,s a Nova. Does this help.

[Chimo]

DF

I fished out a mates Nova at Kingston SE in SA years and years ago and it certainly wasnt running anywhere near the HP you are thinking about. I seem to remember that the fuel was in tubs not underfloor too. Someone will have a bit of old Nova paperwork but I'm guessing that given the hull shape that 75HP would have been optimum and maybe 100HP max in a 2 stroke for the model. Like I said tho, some one on here will have some data for you.

Cheers
Chimo

[FNQCairns]

Dirtfloor got it before me, my wild guess was going to be a Nova.

Sure you have a lot of hp but the beast only unleashes that HP via the throttle same as any modern V8 driven legally on road, so your only true consideration is weight and this means weight at rest on the water, how heavy is a heavy 115/140hp 4stroke? seen lots of them on 17 footers in the past.

So it all comes down to how much buoyancy is at the stern, it looks like you have done a cracker job so far, you might also consider adding some buoyancy at the transom,hull extension buoyancy pods either side or go all out and 3/4/full pod the outboard.

15 foot f'glass low stern buoyancy race boats see this weight and more easily but they only sit on lakes/rivers, offshore the weight would make them a pretty pretty hairy recreational fishing choice.

!00km/h+ here you come :)

[deckie]

The reason i say not to get on the gravy train of hull mods to carry the donk is you should be able to sell the 225 and switch to a more suitable donk without losing any $. Plus you've done all that work already.
Thats of course unless you like the idea of having the very first 60knot Nova half cabin :D The kids would certainly be screamin on a biscuit :D...then its out to the 10 mile reef in 7 minutes, then back in downwind in 6 minutes and let it really crank in flat conditions back to the ramp :D She'd be a handful though i reckon ;D

hey fnq..u saying u have the discipline not to use the grunt lol ? ..there's no way in the world the average hoon like me and the next guy wouldnt want to at least see what she can do ;D

You blokes sound pretty sure its a Nova. I'm just guessing.In the absence of knowing for sure, some more pics would help, including original interior layout and transom.

[Jarrah Jack]

Whether its a Nova or something close I doubt there would be one boat of that size from that era, 80's? that would be rated for that size donk and more than likely weight as well.

The transom may need more strengthening to take that weight. Insurance is the big thing, if you want to insure the boat. I suspect that you will need to have the boat signed off by a pro to keep the insurance company happy. They don't mind taking the money but when its time to give some back then they'll be looking for an out.

The fuel use would be interesting but the range you'll get from,say, 100 ltrs while keeping some in reserve may be more of a concern.:o

Beautiful job btw. Well done.

[sharkymark2]

I had a nautiglass 15' and put a 90hp eveinrude on the back and it was always tail heavy at rest. Got a scare a few times with waves getting a bit high over the stern and filling up the well. Later I found that it was rated to 85hp. Yes it did go quick but chiro visits are a tad expensive after you add up the fuel bait hooks and sinkers etc etc. I think you would be crazy to put it on. Bad mistake. I begin to wonder why we want such big HP's when most of the time the weather is so shitty that we throttle back. The fuel bill almost doubles once you get to WOT so why not take it a tad easier and enjoy the scenery and save some big money from going to those thieves who peddle petrol.

[Chimo]

Hi Sharkymark2

Just guessing but if you had a 90HP Evinrude that was a vee 4 and in that case you might as well have put a 115HP on as they both weigh in at 167kg or there abouts. How do I know that? I had a 90 on a previous boat and now I have 2 115HP of the old style. Nothing much worse than the water over the back thing!

So DF I think I'd stick with the 2 stroke 75HP max or if your going 4stroke maybe about 50HP ish from a weight point of view.

Cheers
Chimo

[Moonlighter]

Found a link to a very similar looking Nova 5.5 half cab and it's got a 135 HP outboard on it's transom. See

http://www.boatstobuy.com.au/power_boats/nova_half_cabin.7227.php

I'd think that a reasonably recent model outboard up to about 140 HP would probably be as high as you'd either need or want to go on such a hull.

Cheers

ML

[Dirtfloor]

Thanks Moonlighter, it's the same boat only I took the cabin partition out and I don't have a pod. Would the pod allow for a bigger donk.
I think I'm going to follow Deckie's advice and try to sell my 225 and get a 140 or something. I've done plenty work on the hull and I don't feel like doing more. I NEEED to get on the water!!!.
Anybody have an idea where the best place to advertise or should I try my luck on eBay? As always, you guys are great with the feed back. Wish I had found this site before I started.

[deckie]

df...dont be thinking straight HP..think power to weight as well as what u want from the rig.
Difficult to repower older design hulls with 4 stks due to weight, till recently almost impossible to do it without compromising the hull's performance. At the same time with 2 stks, if dropping 10-20 hp HP at the transom can save 20-40kg its often beneficial to the hull's performance.
Are u planning livey tank down back ? There's another 30-60kg or more alone. Heavier motors reduce your capacity for mods and options.
Where's the fuel now ? Would a bit extra range be useful to get to the area u want ? biggish 2stks can drink fuel as u know, in which case where do u carry this ?
Planning a dual battery system ?..bingo another 20-30kg on the arse.
Adding a baitboard ??..that can weigh another 10kg over the motor to start ?
On older hulls designed for lighter 2 stks these type of things were never in the original manufacturers design/hp rating/transom weight specs and need to be considered additional transom weight effecting perfromance.
Plus of course the added wrenching/torsion on a transom not designed for big hp aint always smart.

How many guys u planning to carry?..are they big units or kids ? You dont want it to feel a bit back heavy just having 2 sizeable guys walking down back.
It all adds up and the transom is the last place u really want it all hanging...every 10kg right at the back on a 5mish rig means less effective hp and more fuel for a 2stk.

Was this hull meant for speed anyway ? With the mods to the hull you;ve done what do you estimate is the overall weight increase ? Just flowcoating the inside can add 15kg, let alone redoing underfloor...that might sway to a bit more HP.
What do you normally see put on these hulls ?..any real reason to go any bigger ? Using it for the odd bit of skiing or just fishin ?
All things to consider.
Just saying dont assume even 140 HP is necessary...a LIGHT 140 would obviously be sweet but do they exist ? Maybe if u can save another 20-40kg on a 115hp then she might even end up a better boat in a following sea with little change in overall performance, but good gains in balance and performance.
Make further enquiries..even tracking down guys with the same rig.

Dont assume any for sale with 150's or 4stks means they can take it, coz they could be arse heavy nightmares and being offloaded for that reason. Many many boats out there for sale that are arse heavy coz little planning went into a repower.
You really need to track down the transom specs/hp/weight as a start if dont know.
Also now is the first time u could truck her down to a weighbridge if hull is finished, if u know the trailer wieght u know the hull weight without the donk and that can help a decision. Remember there'll be a massive difference when fully loaded for a day out and weigh again later. Then Length X Transom Width at Waterline X 16 - 67 X 1.34..its a rough starting point to work up from. Heavy donks have a habit of reducing your future options. Dont need it, dont put it on.

[deckie]

Also df..u can get a rough idea of WOT speed you would be looking at with each motor, which might help a decision ...thats IF you can resonably guess final weight loaded.
At this point tho you'll need to weigh the hull, add wet motor weight of the one you;re looking at, add fuel weight (can be done accurately for your tanks), your weight or crew weight, then add rough weight for extra's u carry. i.e. if u can do a bit of maths to get a best guess loaded weight on the water heading out for a fish. Best guess stuff whilst unfinished but could help a decison on motor.

Crouches planing speed forumula says Speed = Drag Coefficient / (sqrt( weight(lbs)/hp at shaft)). Gives an answer in knots and fairly accurate. For drag coefficient they use 150 for heavy hulls, 170 for average hulls, 190 for lighter/faster hulls, 210 for racing hulls. I'd use maybe 165 or 170 for coefficient and solve basis imperial measurements. Deeper the V the lower that coeffient. i.e 20deg deadrise maybe use 160, 10 deg deadrise maybe use 170-180, flat bottom punts more like 190- 200.

[Chimo]

DF

What deckie says and I suggest you re-read post 9 again and check out for example a 3 cyl 75 HP or a 90 HP with the same weight in an E- Tech In the old carbie models the 90HP Evinrude is the same weight as the 115HP both of which are damn good motors and cheap these days.

Cheers
Chimo

[Dirtfloor]

Thanks Guys,
Deckie, I think I'm going to have to go to Uni to work out all those numbers you gave me. My eyes have glazed over!!!
The plan is to go fishing mostly with the occasional ski. I've got four kids but they're adult and left home so if they all show up it will only be for a cruise in enclosed waters. Otherwise it'll just be me and the minister of home affairs going for a fish.
As I understand it, 90 to 115 would be my best option as the weights are similar and with enough hp to have fun whilst staying safe. I don't have a lot of money (truth is I don't have any) so I'll be going for an older 2 stroke. I've got a sixty litre fuel tank which sits under the splash well. By the sounds of I'll need another one and probably move it amidships. I did plan to weigh it before I put the motor on and I know the trailer weight, so I'll have all the specs.
I'll put the 225 on eBay and see what happens.
Thanks again.

[Jarrah Jack]

Dirtfloor You're not related to Muddy Toes are ya?

[Moonlighter]

Hi Dirtfloor

There is another probably easier guide to work out max hp for your boat. The "Australian Standard for Recreational Boat Building AS 1799.1 of 2009" includes a formula that builders of boats have to use to determine the max hp for their boats. Once they apply the formula, they then have to do an on-water test that is also in the Standard and the boat has to pass that test without getting any water on board, otherwise the max hp produced by the formula has to be reduced.

Anyway, for your purposes, you could apply the formula to your boat and see what the answer is, and that will give you a pretty sound guide as to the max hp for your boat.

The formula, as per AS1799.1 (2009) is as follows:

Step 1. Multiply the overall length of your boat in meters by the width of the boat at the transom (at the waterline). that gives you the "factor".
Step 2. Multiply the "factor" by 16, and then
Step 3. Take away 67
Step 4. Then multiply the result from step 2 by 1.341 (this converts the previous result from kw to horespower)
Step 5. Round up the result to the nearest 5 horsepower.

So, for your boat the pod could be included in the overall hull length, so to give you an idea as to how the formula works, for your Nova it could look something like this:

Overall Length = 5.5m, plus pod another 300mm = 5.8m (you should measure the actual length to check)
Beam at transom at waterline = say 1.9m (again, you'll have to measure this to get the actual beam)
So applying the above formula to these measurements would go like this:

Step 1: 5.8 x 1.9 = 11.02 (this is now the "factor")
Step 2: 11.02 x 16 = 176.32
Step 3: 176.32 - 67 = 109.32 (power in kw)
Step 4: 109.32 x 1.341 = 146.59 hp
Step 5: round up to nearest 5 hp = 150 hp

Here's the link to the abovementioned Standard so you can (and should!) check the formula, its on page 16 or thereabouts):
http://www.nmsc.gov.au/media/pages_media_files/files/AS1799%20Small%20Craft%20-%20Part%2012-General%20Requirements%20for%20Power%20Boats.pdf

Hope that's clear and helps firm up your ideas about what size engine. Bear in mind other earlier comments about engine weight, those older hulls generally were'nt designed to carry some of the heavier 4 strokes, but also remember that in their day, some of the older 2 strokes weren't exactly lightweights either!

Cheers

ML

[Chimo]

So on the basis of the above data a 115HP 2 stoke (ie Evinrude) weighing 167kg and costing less than 5k for a really good one would be golden! Especially if there is no pod and boat is not 5.8 but 5.5m

C
C

[Fed]

176KW = 131HP then you need new rings.

[Nathan Tuskes]

was thinking the same Fed...wtf.. for my haines it works out at 86units......is that rounded down to 85kw like some of the haines 445 runabouts or is it rounded up to 90hp like the more modern formula f15(same hull mould)???

[Moonlighter]

Edit: sorry guys, got the conversion formula round the wrong way, one (1) kw = 1.341 HP, so need to re- do the calculations above!

Apologies for that...

ML

[Chimo]

Hi Moonlighter et al

A Seafarer Vagabond that is a heavy, podded 6.2 m boat is rated to 230HP and if you use your computations for the 5.5 m boat we are considering, it too is rated to about 230HP. It seems we agree that this is improbable so perhaps something could be amiss with the comps. Thoughts?

Cheers
Chimo

[deckie]

not sure if fleabay is the way to go selling an outboard.

Anyone had a good experience lately selling a motor or could advise where to start ?

I got no idea where's best to sell one these days but guess at places like boatpoint/boatsales/trading post etc

If the 225 is in good nick and you arnt in any hurry, i cant imagine you'd have trouble turning it around for a more suitable donk at zero cost. I'd suggest u will need to carry a bit more than that 60l fuel too..which adds a lot more weight down back also. Just sounds more and more like you;re best to err on the side of a much lighter donk. If u do a bit of research, maybe a few sums, and get the right donk she'll be a bewdy. Good luck.

[Moonlighter]

Chimo

You're right, I thought the formula looked a bit out, went back and checked and realised that I missed out a step (take away 67...), so have amended the calculations in the earlier post, am pretty sure they are now correct. Also included a link to the Standard so you all can check it out for yourselves, which would be a good idea given my earlier poor form!

Cheers

ML

[Chimo]

So

From post 1

"The boat is 5.5 mt half cabin"

Factor is 10.45 by 16 = 167.2 minus 67 = 100 by 1.341 = 134.3 HP max

IMHO I'd still look at a cheap 115 HP v4 approx $5K evinrude / johnson @ 167 kg vs a 140HP 4S @ 186 kg for $16K and keep the boat in character.

Cheers
Chimo

[Dirtfloor]

Hi guys, yeah, I did the same. I checked the standard out and my transom width is 1.7m which works out to a 110 donk. So I'm in the market for a 115 thereabouts evinrude/johnson. I'll check out boatpoint etc and let you know how I go.
Cheers DF

[Moonlighter]

Good work Dirtfloor, sorry to stuff you round with the formula, but sounds like you've got things in hand now. For what it's worth, I agree with Chimo that somethng round the 90 - 115hp range would be very nice in that hull.

I have a Surtees 5.5 and its max hp is 115, and I've got a 115 Suzuki 4 stroke on her and she flies, plus is very economical. FYI, I get about 2.25km to the litre from the Suzuki on average.

So I'd be pretty sure that you boat with around 100-115 on the back would perform very nicely indeed.

If you can get a sub-floor tank in the hull somewhere amidships or between the skipper and deckie's seating positions, that would add to the balance. Something around 100 litres, give or take, depending on how far you intend to travel and whether you go for a modern 4 stroke or DI 2 stroke like an E-tec or Optimax (or even a Tohatsu TLDI - my last boat had one of them, a 90 TLDI and had heaps of power and very impressive fuel economy too). If you go with a old-style 2 stroke you might want a bit more fuel capacity than that, to counter the greater fuel use and still give you decent range..

Cheers

ML

[deckie]

Still need to measure for right shaft of course coz we dont know if those hulls are anything out of the ordinary, so check bottom to transom cap height where donk will sit in inches.
Looks like best guess from everyone's inputs is that a 115 would get her along alright. If u see a 130 rude v4 i think they weighed the same/similar as the 115's. Something worth checking coz i might be wrong, someone else in here might know..the 110-130hp region sounds about right to me for a 5.5m half cabin, which from the input of others is around the 160-165kg. Perhaps u could set that as your transom weight guide, and research donks in at or under about 160-170kg.
Like moonlighter says fuel is a bit of an issue of course...and it weighs. You really do need a capacity to carry 100ltrs+ with those donks.
How much does a merc 4 stk 115 weigh ?

[Dirtfloor]

This has been a steep learning curve. And much fun too. I'll research and keep posting. Thanks again

[Chimo]

DF

Empty your PM box!!!!!!!

Its full so you cannot receive any more PMs

Cheers
Chimo

[stue2]

Seems these guys have well sorted DF. So for whats its worth I have a vote for the 115 size. You wont need any more than that and you wont want 100lt fuel down back either. But you will want 100lt.

Cheers, Stu