Long shaft motor on standard shaft boat?

[Dtwo1946]

Hi.

I've got an Aqua Jeep 430 fitted with a Yam 50hp two stroke long shaft motor. The boat is designed for a standard shaft. The Yam is mounted on a substantial marine ply transom that is bolted to the original fibreglass transom so that the motor, when mounted on to the ply, is raised 3" to simulate a standard shaft arrangement.

I'm not too happy with this as even marine ply deteriorates eventually and a 50hp beast leaving the transom at speed is no joke. My easiest solution would be to remove the marine ply transom and refit the engine to the original transom but...

...what effect will the extra 3" of shaft have on the performance of the boat? I use it mainly for fishing on my local river but I have to admit that the existence of the 5mph limit occasionally slips my mind! However, I don't use it as a speedboat. Who the hell can afford to thrash a two stroke with the insane cost of fuel these days?

Does anybody know anything about Aqua Jeeps? There's a nice 75hp force with PTT for sale at the moment and as far as I'm aware the Jeeps were rated up to 80hp. However, the Force is already on an Aqua Jeep and the owner is selling it because he says it's too big for the boat. Evidently the bow points to the sky when the motor is fitted. Can anybody enlighten me?

Thanks

 

[landlockedpirate]

Welcome to the forum.

Fitting a long shaft on a short shaft transom (i.e. dropping it from its current position) will cause problems. The type of problem will depend on multiple factors including hull shape, transom rake and shape of the gearbox casing and cavitation plates. These problems could be as minor as a little extra noise or spray to dangerous handling characteristics.

I presume the engine is already bolted through the marine ply extension into the original transom and the built up part is actually taking very little weight or pressure. My feeling would be to leave it alone unless there are obvious problems with the extension piece, moving the engine could well cause you a whole list of headaches. This is especially true if you are using the engine mainly for low speed work.

Not sure why you would be looking for a bigger engine if you are already concerned with the existing 50hp fuel consumption. I would only be looking to put an engine that big on a 4m boat if I was using it for watersports or if it was heavily loaded.

 

[Spi D]

Fitting the engine higher on a small boat even will challenge the balance due to higher point of gravity.

I'd opt for a correct length engine. Preferably 4-stroke. Loved my Suzuki (last boat before switching to shafts).

 

[landlockedpirate]

I'd opt for a correct length engine. Preferably 4-stroke. Loved my Suzuki (last boat before switching to shafts).

The problem with a 4 stroke is weight, this boat was designed in the 70's for 2 stroke power. Sticking a heavy 4 stroke on the back will virtually swamp the transom.

 

[Spi D]

A 2-stroke 50 hp Evinrude or Yamaha is stated to weigh 190+ pounds dry. A 40 hp Suzuki 4-stroke weighs 224 (long leg, short will be less).

On a boat this size I'd happily accept the extra weight and suffer 10 hp (nominal - if the old one is flywheel hp the difference to modern prop shaft measuring ie. will be less) to gain the pleasures in running quality and fuel consumption.

All else equal, of course. Money might be needed between the two and no gain in mpg will ever pay for the engine.

 

[Dtwo1946]

Thanks Mark. Yes, the marine ply extension is bolted through. However this is my concern. There are four mounting points on the engine bracket. The bottom two bolts on the bracket are through the marine ply and the original glass transom. Another two mounting bolts have been added that don't hold the engine. They go through the marine ply and the original transom and serve to secure the marine ply only.

The top two fixing points on the engine bracket go through the marine ply but are above the original glass transom therefore these only hold the top part of the bracket to the marine ply. This is the possible weak point that I'm concerned about. After reading your comments I think I'll just persevere until I find a 50HP standard shaft with PTT. Problem is the yam I've got is bullet proof and any second hand engine is a risk.

The only reason I was considering the Force 75 is that it's a good price and the Yam isn't PTT. If I want to troll using an electric motor the lower leg is a drag (it's almost impossible to lift from inside the boat). An electric doesn't have the range to get me upriver from the slipway and troll so I need to start out on the Yamaha.

I don't want to fork out for a 4 stroke even though I take the points made in later posts about the advantages.

Thanks again.

 

[landlockedpirate]

I would be careful with the force, they are not the best engines in the world, actually i'm being polite, they are bloody awful. The later Mercury based engines were better, but the earlier Chrysler based units were pants, thats why it seems cheap.

 

[ontheplane]

I would be careful with the force, they are not the best engines in the world, actually i'm being polite, they are bloody awful. The later Mercury based engines were better, but the earlier Chrysler based units were pants, thats why it seems cheap.

+1 - I Owned a Force 75 once, I honestly think I didn't EVER have a whole weekend when it didn't break down at least once - bloody awful, if I saw a boat with one on for sale, as far as I was concerned I would knock off the cost of a new engine

 

[Dtwo1946]

Thanks. I had my suspicions and I'll keep well away from it.

 

[Dtwo1946]

Thanks.

 

[Nick_H]

So;

There's a 5 mph limit where you use the boat
the 2 stroke 50 hp is already too heavy for the boat
You have a long shaft when you need a short short shaft
You're concerned about fuel consumption
You carry a seperate electric motor for trolling

Why not sell the 50 hp, and the electric trolling motor, and buy a small 4 stroke that will do the job of both quietly and cheaply? I don't know the boat, but at 4m i'd have thought something like a 15 hp would do that comfortably, maybe even a much smaller engine would be OK. If the speed limit is not enforced, and you want to be able to plane to get to your fishing area quickly, what's the smallest engine that would sensibly get you on the plane?

 

[Dtwo1946]

Hello mate. Thanks for replying but let me explain.

I use the boat mainly on the Tees where (officially) it is restricted to 5mph but it also goes to the Lake District, Scotland and to sea off Whitby and Teesmouth fishing for Mackerel deadbaits. Anything below 35-40HP would not be wise. 15HP would be suicidal. The tide rip off Whitby can be fearsome and I wouldn't be happy with less than 50.

My two stroke 50 isn't too heavy for my boat. The owner of the 75HP Force that is on HIS Aqua Jeep says his engine is too heavy. The Aqua Jeep was designed as an inshore rescue boat and as such, being a cat, is very stable with loads of deck space for it's length. Also, in this role it needed power and was rated up to 80HP.

I have a long shaft but the boat was designed for a standard shaft. The transom has been raised to simulate a standard shaft arrangement.

My comment on fuel consumption was a 'tongue in cheek' reference to the price of fuel in the UK. I'm not really bothered about £20 spent on gas and oil.

My query was 'what will be the result if I bolt my 50 straight on to the original transom thereby adding 3" to the length of the lower leg?'. The boat is pretty rapid powered by 50HP.

Regards

 

[Spi D]

It is not going to be easy to swap a so-so Yammie long leg to a better engine with short leg without forking out something.

Chrysler fell over and out of the ashes came FORCE as Brunswick Corporation's attempt to get a cheap alternative to their main brands Mercury/Mariner. By doing so, repeatedly attempting to remedy the worst of Chrysler's design flaws, they wanted to be able to offer boat+engine+trailer packages on an entry level. Mated to eg. early Bayliners, shipped on a craddles with wheels (they called them 'trailer'), many was sold as seemingly very good value.
Before long the FORCE got the unflattering nickname "F*ckingOldRenamedChryslerEngine'.

Your quest might take you by late generation TLDI 2-strokes from Tohatsu (the company that make the majority of small outboards sold under major names) and Evinrude. Evinrude's E-TEC series brings a new standard to the world of outboards, including simplified maintenance.
Never owned one but fellow boaters talk highly of them.

 

[Beamishken]

My query was 'what will be the result if I bolt my 50 straight on to the original transom thereby adding 3" to the length of the lower leg?'. The boat is pretty rapid powered by 50HP.

Regards[/QUOTE]

Id bolt it on & try it an extra 3" in length wont make a major difference apart from knocking a few kts off your top speed if you use the top set of hounting holes on the transom bracket you will end up somewhere between long & short shafts anyway the engine doesn't have to sit tight down to the top of the transom as long as you get 4 bolts into it & they aren't too close to the top edge of the transom it wont go anywhere just sit it on a piece of 2x2 or similar till you get the bolts in

good 50hp 2 stroke yammies are hard to find & you will struggle to get another engine as reliable as a yam 2 stroke

at least if an old yam works itself you wont need a laptop to diagnose it!

if your ok with the fuel consumption give it a try & see how it handles just be carefull not to trim in too far as that can make handling strange if the engines too deep

 

[Spi D]

If you find a short Yammie with matching leg, simply move the short leg to your engine. Nominal difference is 5".

Keep the old one for spares.

 

[Dtwo1946]

If you find a short Yammie with matching leg, simply move the short leg to your engine. Nominal difference is 5".

Keep the old one for spares.

Thanks. I'd considered this and I think you're right.

Ken Nunn said it all in his last post. The Yam 50's were terrific engines and good ones are like hen's teeth. Mine is bullet proof so rather than take any silly risks I think I'll keep my eyes open for a shorter leg and do a swap. In the meantime I'll take Ken's advice, drop the motor on to the original transom, then drive around gingerly to check out it's effect.

I'll also be looking for a power tilt unit for it but these are rarer even than hen's teeth. The correct part for this motor doesn't have the two trim rams. It just has the main tilt ram and the motor. I know this because I bought a mint but later second hand unit with the twin trim rams which, of course, was as much use as a one legged man at an arse kicking party. However, I managed to sell it on and got my money back.

Foolishly I called Power House Marine in Newcastle to price a new unit. The bloke I spoke to looked it up and just said 'no no mate, It'd be cheaper to buy another engine' so that's a non starter.

 

[AndieMac]

I've seen retro-fitted transom height extensions to fit longer shaft high-powered outboards fabricated from a large slab of heavy gauge stainless steel plate attached to the outer aft edge of the transom, around 400 x 500mm, even larger depending on the engine.
The outer plate forms the aft edge of the fully welded up box section to sit on top of the existing upper edge of the standard transom and is attached with through bolting and sikaflex.
As long as the original transom is strong enough, with no rotting internal timber for instance, these extensions appear fine.