Do I need to lower my motor?

[Dry Diver]

I took out my 16' achillies today with a 40HP merc, 2 stroke. At anything above 1/4 throttle the prop was cavetating like crazy. I tried all the different settings for trim (manulel trim on the motor) and had no affect on the performance. I was able to get the boat to get on plane. Though soon after the motor would start to cavetate. I also tried having my girlfriend move about the boat to distribute the weight differently in the boat, no affect.

I have a short shaft motor, should I cut the transom (wooden LVL style transom) down to lower the motor in the water more? What should I be looking for? How far below the water line should the center of the prop be?

Also I have a three blade prop the pitch is 15. Is that the right prop for the motor?

Thanks in advance for all the help.

 

[jimandsue60]

Re: Do I need to lower my motor?

Achilles web page shows a long shaft required for current boats above 14 feet. I would hate to have to cut on the transom but it will be cheaper than replacing the engine.

Jim

 

[Dry Diver]

Re: Do I need to lower my motor?

The boat that I have is a 1984, I was told that it needed a short shaft motor. Not sure though I will have to contact Achillies to be sure. You are right though it will be absolutely cheaper to cut the transom than buy a new motor.

 

[kandil]

Re: Do I need to lower my motor?

Are you sure it is caveatting? you might have a slip prop that is from a bad rubber hub mark the rubber and the bolt and after it does act up check your mark. good luck oh and don't cut the transom

 

[Dry Diver]

Re: Do I need to lower my motor?

Thanks for the advice. I Will check that tomorrow and let you know what happens.

 

[Dry Diver]

Re: Do I need to lower my motor?

Are you sure it is caveatting? you might have a slip prop that is from a bad rubber. good luck oh and don't cut the transom

Well I checked the prop and hub. There is a nylock with a washer with tabs that bend up under it that is keyed onto the prop and shaft. I think that would eliminate the prop from slipping.

So I did the unthinkable.....I cut the transom.

I brought it out in the lake today and I have to say.....HOLY CRAP. what a difference. The motor ran great and did not cavitate once. It jumps right up on plane and will stay there at much less than 1/2 throttle. Very happy with the performance. Works great!

 

[jimandsue60]

Re: Do I need to lower my motor?

I don't think it is that unthinkable, you gotta due what works for you! I am glad it worked for you. Can you share how you did it maybe post a picture or two.

Thanks
Jim

 

[Dry Diver]

Re: Do I need to lower my motor?

Can you share how you did it maybe post a picture or two.

Thanks
Jim

All that I did was make a line parallel to the top of the transom 2" below the top of the transom where the motor originally should have been mounted. Measured the mounting bracket on the motor. It measured 7 3/4" so I centered it then made the vertical cuts down the 8" wide so I would have a little "wiggle" room. End result, the motor is now mounted 2" below where it "should" be, lowering the center of the prop another 2" in the water.

I will have to wait on the pics. I don't have m camera here with me now. I will put a coat of epoxy over the top of the transom where I cut to reseal it then I should be good.