65HP 2 stroke vs 60 HP 4 stroke

[jhmtaylor]

I have a 4.9M custom aluminium boat which I am about to refurbish. The current motor is a Suzuki 65 HP s stroke which is 14 years old and needs replacing. The boat is rated to 70 HP but I do not think they were taking into account 4 stroke motors which weigh upwards of 170Kg.
I need to put a new motor on and my question is "If I went down to a 60 HP 4 stroke would I notice much difference in performance" Also Mercury have a 60HP 4 stroke bigfoot. Do they have more grunt than the standard Merc 60HP? I have no specific preference for brands so performance then price will be the decider.

[Giffo65]

I have a 60 hp Yammy 4 stroke that is a High Thrust.It spins a bigger prop and has a lower gearbox ratio I think.I have used it to tow blokes to go Scurfing no probs,seems to have low down grunt.My hull weighs about 380kg bare,its a Polycraft.

[Tickleish]

Yes you would notice the differance in performance. The Merc bigfoot has different gear ratio's so it can run a bigger prop (I Think?) I've never owned one but they should have alot more grip in the water with a bigger prop but IO still don't think it would match the old Suzi.

why don't you buy a new two stroke? It would be heaps cheaper and they hardly chew any fuel in that capacity anyway.

It would take 1000hrs before you made up the money differance of a 4 stroke.

[wayno60]

The new 70 yamaha 4 stroke are only 119kg, $10,200 on ya boat ready to go....

[cormorant]

The old Suzuki 2 strokes were a Ok uncomplicated motor and made good power. Why does it need replacing and how many hours and what sort of work are you going to do with it in what areas? A few hours a week , with loacal VMR about and not well wide offshore without a auxillary I would see if the old Zuk is worth keeping a while if in good nick. Being a custom boat you really need to put it on the water and add a couple of sandbags on top of the motor and just see how it rests in the water with a fully loaded boat ( extra sandbags or a couple of mates etc) for a start and take a couple of photos.

Is the custom hull builder still in business or is their sisterships of your hull shape about on boatpoint etc that you can call and have a chat to another owner with a different motor choice?

How did the boat perform with the 65hp on it?
If you are doing a refurbish and spending coin on a new motor is it worth doing a pod or other arrangement to rerate teh hull to take a heavier motor?

Just a few left field thoughts

[jhmtaylor]

The existing motor is 14 years old and whilst it runs OK, parts are getting hard to find. It probably has less than 600 hours of use. With 3 up it had no trouble getting up on a plane at 17 knots on flat water. It is a heavy boat for it's size weighing around 550Kg ex motor. In a steep sea with the bow already up in the air it struggles a little. I will try the sand bag suggestion but I think it will handle an extra 25Kg OK. The extra 5HP of a Yammie 70 would be good.
I would prefer a 4 stroke because the resale ability of a 2 stroke is bad

[cormorant]

The 5 hp may only be at the top end. You need to think about the torque / hp curve of the motors you wish to compare. The real important point is the cruise hp and torque at those revs as that is where you spend your day not on full throttle normally. Would the builder or if he is unavaliable a marine surveyor rerate the hull for either more hp or weight so you have more options.?

Propping may make a huge diference as would pods to take weight if it doesn't feel right. Add the 5 kg plus plus for a stainless prop and oils and bigger battery depending on how they quoted the weights.

Tohatsu probably make the bargain motor in that range as a 2 stroke .

[maimai]

Your 14 year old 65hp would be rated at the fly wheel not at the prop (50hp at prop at the most) The merc big foot has great mid range torque, If your boat is rated 70hp than find any 70hp motor and get it fitted


That ol 65hp weighs about 100kg, i would go with Wayno;s post, go the 70hp Yamaha

[Tickleish]

they changed the hp rating in the early 80's.

[jhmtaylor]

That ol 65hp weighs about 100kg, i would go with Wayno;s post, go the 70hp Yamaha
I concur, good discounts available on the Yammie at the moment.