I have a 1994 Avon Seasport 5.45 powered by a 90 HP Yamaha 2 stroke. Engine weight is 266 lbs.
I would like to repower with a four stroke 90. Its weight is 377 lbs.
Are there any issues I should be aware of?
I've looked online for hours and can find no answers, so any comments would greatly be appreciated
Apart from the engine maybe being too heavy for the transom and causing damage, that extra weight might really upset the handling of the boat, especially in a rough sea.
The Stern will drop into every trough when coming off a wave, and will be sitting lower in the water so will corner differently.
You might find the transom swamped when you come to a rest as well.
You might regret doing it, but unfortunately the only way you'll know is to do it.
If you go for it you'll need to be ensuring at the very least that the timber in the transom is still in tip top condition with no rot and the Laminate is still firmly attached.
As mentioned above I'd also be adding some extra knees.
I ruined the handling of a RIB with a too heavy and powerful engine, but wanted the straight line speed and learned to live with it. If you are prepared to compromise on handling etc to gain better fuel consumption I'm sure you'll adapt
If you need a four stroke, Yamaha's latest F70 is about 262lbs (119kg). I would be very careful increasing the weight by a lot more, as has been mentioned here.
I'm loath to recommend them typically but a hydrofoil might prove helpful too by lifting the stern higher, avons really have an issue with weight at the back, just moving the fuel tank up made the world of difference on my sr4. Either way it's all just sticking plasters over a core issue that the engine's just too dang heavy. a 90 e-tec is 320lb which might be worth looking into
Zodiac
