Yamaha 70hp or 75hp?

[sturgeon]

Yes. It's a 4 stroke.
I'm looking at a streaker 4850.
I just realised that if it can take a Yamaha 75, it shd be able to take a 90 Hp as it's the same engine. The 75 is basically a detuned 90hp. Both weigh 161kg which is about 40kg more than the 70 Hp. Some people say that the additional 40kg plus puts too much weight on the transom making it sit too Low in the water. I assumed that also means difficulty in getting the bow done as a result.

[bowl]

Max 70 4 stroke n max 90 2stroke
http://www.streakermarine.com.au/4850-navigator

[frozenpod]

Based on the specs and passed experience I would suggest the suggested lower 4 stroke power is purely due to the weight.

Most of the 4 strokes are around 160-170kg and keep in mind it is possible to balance the boat with a heavier outboard. IE average size batteries are approximately 20kg each. Moving 2 batteries from the back to the cabin would offset most of the weight.

I would see if you can go for a water test so you can get some idea of how it performs.

PS I would almost certainly fit a 90hp motor and I would probably go for a 2 stroke due to the weight.

[sturgeon]

Max 70 4 stroke n max 90 2stroke
http://www.streakermarine.com.au/4850-navigator

That was before the Yamaha had a 75 accordingly to the dealer.

[sturgeon]

Based on the specs and passed experience I would suggest the suggested lower 4 stroke power is purely due to the weight.

Most of the 4 strokes are around 160-170kg and keep in mind it is possible to balance the boat with a heavier outboard. IE average size batteries are approximately 20kg each. Moving 2 batteries from the back to the cabin would offset most of the weight.

I would see if you can go for a water test so you can get some idea of how it performs.

PS I would almost certainly fit a 90hp motor and I would probably go for a 2 stroke due to the weight.

No water test available and I could not find any performance bulletin. And one dealer recommended the 70 (transom sitting too Low) and two recommended the 75 for "more grunt" and "skiing".

[frozenpod]

The yamaha 75hp 4 stroke is the same motor as the 90hp just detuned.

Since two dealers have recommended the 75 it sounds like that boat can support the weight and I would go for the 90hp.

IMO there is no point other than saving a few $$$ to fit the detuned version of the same motor.

In 12 months time you will forget about the $$$.

[bowl]

Go test a second hand one

[Mattblack]

[frozenpod]

Not quite Matt, boats of this size have typically been fitted with 90hp 2 strokes for 30 plus years.

It wont be a rocket ship with a 90hp motor but will provide acceptable performance.

PS General rule of thumb is 80-100hp per 1000kg. Full tank of fuel, 4 People on board plus gear this boat would be around 1200kg on the water. Fitting a 90hp motor is equivilant to 75hp per 1000kg ie a bit under done.

[ratbag]

if 40kg makes that much difference, what happens when you load it with people & gear? like the others have suggested, you may need to 90hp to move it along comfortably. smaller engine will always work harder than the bigger donk.