Engine height question. Inflatable

[Drowned Rat]

Hi guys. I've got an Achilles 14' inflatable with the inflatable floor and wood floor boards. I'm using an 8hp Yamaha 2 stroke on it. I know it's underpowered for this boat, but it does plane easily with one person and not so easily with 2. Here is the problem I have. When on plane, the bow, particularly on the right side, wants to dig in and I can see water spraying up in the area of the right side bow. When this happens the boat obviously want to lurch forcing me to slow down. The engine is a short shaft and the transom is made for a short shaft, but the anti-cavitation plate is about an inch above the low point in the hull. Would the engine being too high cause the problem I'm describing?

Next problem is how do I fix it without buying a long shaft motor which I think would be too long anyway. Can a jack plate be installed upside down to actually lower the engine a little? Can I cut the transom down about an inch? What about those spring loaded jack plates, would it be strong enough? I eventually want to put a 20hp 4 stroke on this boat, so whatever the solution, I would like for it to work for the 20hp as well.

Any ideas?

 

[mystro]

Re: Engine height question. Inflatable

Try a whale-tail fin on the motor, if it works to correct this problem its a cheapo fix plus it will really help you plane easier regardless..it's almost like having trim tabs.

 

[Franky219]

Re: Engine height question. Inflatable

Hello, I had the same problem with my 12 ft Zodiac. I put Hydrofoil on and it solved my problems. I'm running a 1972 Evinrude 9.5 on it and it wouldn't
plane out until almost at full throttle. With the hydrofoil I'm on the plane at half throttle with 2 people and a full gas tank. I also had a problem with prop blow by and the hydrofoil cured that too.

 

[deejaycee_2000]

Re: Engine height question. Inflatable

damn ... yes a 8hp is way underpowered .... you should be at least running a 25hp ...... but those 8hp yammies are great and strong ...... you can try a while tail, but ideally the ant-cav plate should be flush with the bottom of the boat ...... the jack plate idea is not good ..... when do you plan to put the 20hp on it ..... cause if it is any time soon I would just try a whale tail for now ...... the 20hp will fit it perfectly .... as long as it is a yamaha ......

 

[Drowned Rat]

Re: Engine height question. Inflatable

Thanks for the replys guys.

Deejay, It'll probably be a year before the 20hp comes along so I really want to figure something out in the meantime. When on plane, the prop is literally just barely below the surface. I'm not sure a doelfin will work. I'm not even sure if it'll be touching the water when on plane. I guess it's worth a try.

Thanks for the help.

 

[TOHATSU GURU]

Re: Engine height question. Inflatable

Stick a foot long piece of 1 X 2 on top of the transom to get the engine another 1" out of the water. Chances are you are actually to low.

 

[jnewtonsem]

Re: Engine height question. Inflatable

I've got the opposite problem. Have a 15 ft Avon, just upgraded to a 40hp Mariner (Yamaha) with a Stiletto SS prop. The Cav plate is about 2 inches below the bottom of the transom. At original settings motoor was plowing and throwing water into the back of the boat. Increased tilt angle to 2nd highest, it runs much better but concerned that the bow lifting prop and light bow will push bow too high and possible blow over in windy conditions. Have thought about raising motor with a 1x2 as suggested above but will raising the motor like that make motor less secure on transom. It is currently secured by clamps and I don't want to bolt the motor because it makes set-up/take-down harder. Thanks

 

[TOHATSU GURU]

Re: Engine height question. Inflatable

Inflatable boat manufacturers build boats and engine manufacturers build engines. You would think that they would all be on the same page, but they are not. If you have a 15" transom it is a given that any Japanese short shaft engine is too long because their short shaft's generally run between 16 and 17 inches. Couple this with an individual boat's handling characteristics, water conditions and the boat operator's expectations and you get a pretty wide range of wrong and right. Usually you must put a block on the transom to achieve any kind of performance, but there is a point where safety intrudes into performance. Only you can decide where that point is. I have never seen a boat where 1 inch was a safety hazard, but anything above that might very well push the limit.

 

[deejaycee_2000]

Re: Engine height question. Inflatable

you can install a transom elevator, it is basically just an extension to the transom that you bolt on, so you can clamp the motor on and off easily ....

you can even make it yourself if you have the eqp ....

http://www.trmarine.com/cats/pages/trnel.html