shaft length honda airdect 3.2

[smithash]

Greetings everyone.

I have a honda 3.2 airdeck and a yamaha 9.9 standard shaft 2 stroke (actually is been upgraded to 15hp) my question is is this the correct shaft length for the boat.

The reason being that last year I used the boat on Lake Garda and experienced a lot of cavitation etc which I never had with the previous engine a 8hp Yamaha 4 stroke.

There is some slight chipping on the prop which I will replace this summer but any info welcome as I have searched the honda sites to no avail

[br1anuk]

Originally Posted by smithash

Greetings everyone.

I have a honda 3.2 airdeck and a yamaha 9.9 standard shaft 2 stroke (actually is been upgraded to 15hp) my question is is this the correct shaft length for the boat.

The reason being that last year I used the boat on Lake Garda and experienced a lot of cavitation etc which I never had with the previous engine a 8hp Yamaha 4 stroke.

There is some slight chipping on the prop which I will replace this summer but any info welcome as I have searched the honda sites to no avail

I have owned a Honwave T32 and it was a great boat, I used mine with a Mercury 15hp 2 stroke short shaft which weighed 37kg. I had no cavitation problems with that setup, however when I changed the boat to the larger T38 I experienced exactly the same problems your having.

Now I may get shot down in flames, but I think because the boat is setup for the much heavier 4 stroke Honda's the boat has "too much" bouyancy at the rear and is lifting the prop up out of the water.

The only thing I can suggest is try moving the fuel tank and any other gear to the back of the boat to keep the back down.

Hope this helps.

Brian.

[smithash]

It might be that but I am pretty heavy 100 kilos and sit at the rear of the boat so should weigh it down a fair bit.

I am considering replacing the boat and engine with something bigger and quicker but this summer funds are tight so I guess I will replace the prop and see if that improves things

[raymillard]

Before you spend any money, try moving the tilt angle out one notch and see if that improves things. Sometimes if the shaft is set too close to the transom the turbulence of the water will give unexpected cavitation. If you set it out too much tho the boat will drag along bows high for ages before getting onto the plane.
Worth a try though.

[Goinfishin]

Hi smithash I'm sorry I cannot help with your problem but I am interested in how your engine was upgraded from a 9.9hp to a 15hp.

I have a 2004 yamaha FHM 9.9 HP 2 stroke, I really wanted a 15 hp engine but could not get one in good condition. I have looked on some American sites and read that all that was required to upgrade was to change the reed box to the 15 hp version as this is the only difference. i.e my 9.9 is a restricted 15hp.

I enquired at the local outboard shop but they were not interested in "modifying" outboards from standard configuration.

Thanks Brian.

[smithash]

Brian

The engine was already upgraded when I bought it in Germany and I confess not being even slightly mechanical I do not understand how. He did tell me that the 2 engines are the same except for the carburettor so I guess this is a relatively minor modification.

Sorry not to be more helpful

ash

[little J]

I had the same problem with my boat which was a honwave t380 ie inflatable floor but I had a 25hp yamaha 4 st on the back . it would get up on the plane with no problem but then it felt as if there was a air pocket under the back near the transom as soon as this happen the engine would start to slip . I tried everything to stop it happing engine trim , moving weight around the boat but nothing worked which why I sold the boat and now looking for a zodiac futura mk2c or mk2