Transom height and motor??

[dew2]

I have a 14 ft lund WC. My neighbor has the S model,Both have a transom height of 16 3/4 inches.The neighbor has a 9.9HP Johnson shortshaft,It runs fine. I mounted a 15 HP Evinrude shortshaft on mine and at about 1/2 throttle the prop loses grip? it just reves really high and loses traction.Does a transom of 16 3/4 inches seem out of place?? is it too tall for my shortshaft? and require a longshaft?
I was under the assumption that a 20 inch transom takes a longshaft under 20 takes a SS.
Why would my neighbors run fine and mine loses grip?traction whatever it would be called.

 

[pscrabber59]

Re: Transom height and motor??

Your transom ht. is fine with the ss motor you have, but your problem(losing traction??) may lie within your prop & motor, you might want to ck that out first.

 

[dew2]

Re: Transom height and motor??

I have tried it with 2 different Shortshaft motors, The 1988 15 Evinrude and to try another even though the boat is rated at 30HP I tried a 1978 35 Evinrude shortshaft.Both did the same.They seemed as though I had a spun prop,Both props were replaced and I wasted my money buying them (GOOD Price here at Iboats) same results? Thats why I'm stumped.The boat bottom has a straight keel and looks great.

 

[Barnacle_Bill]

Re: Transom height and motor??

Where is the anti-cavitation plate on the motor in reference to the bottom of the boat? It should be within 1" of being even with the bottom.

 

[dew2]

Re: Transom height and motor??

its right even with the bottom of the boat.Another reason I'm stumped.I will try a longshaft this spring,But that will put the cavitation plate 5 inches lower.Thats the 15 even I didnt look at the 35,But both did the same.??

 

[Barnacle_Bill]

Re: Transom height and motor??

Well you have the proper shaft length. Have you tried tilting the motor up or down?

 

[dew2]

Re: Transom height and motor??

Yes but I only tried hole 1 & 2, goin to 3 looked as though it was too high and would raise the bow even more when under power. Of course at 1/2 throttle the bow was really high at 2, but I suppose it would plain out if I didnt have the slippage or whatever it would be called.

 

[steelespike]

Re: Transom height and motor??

Have you checked the plate height on your neighbors setup?I assume you personally measured both transoms?There is nothing different on your bottom compared to the neighbors?
If nothing proves fixable you could try a 4 blade prop they are very effective resiting ventilation.

 

[dew2]

Re: Transom height and motor??

We had the two boats and motors sitting side by side on the trailors and on the dock(we live on a lake) The only difference is horsepower.In the boat I out weigh him by 50 lbs.But I ran his boat thinking that was the difference His with me planes out and the motor works just great.
I rebuild boats and motors as a hobbie,This has me LOST!! I dont know what to do except the longshaft,I am repairing a 25HP LS at the time and will put it on this spring.I will look at 4 blade prop but the cost will limit me! And The shortshaft SHOULD????? work.

 

[steelespike]

Re: Transom height and motor??

The 4 blade Solas Amita 4 blade is $62 here at iboats.They also handle better on plane and at the dock, improve hole shot and stay on plane with less throttle.

 

[dew2]

Re: Transom height and motor??

Thanks I looked up that prop and it is reasonably priced,I have a 10 pitch now and the guide says to drop a pitch so 9 would be the pitch with the 4 blade.Right?
I have the boat keel up now and am checking for loose rivets or any small obstruction that would create bubbles along the way to the motor.Its just a shot in the dark and I really cant do much till open water.Its just on my mind! and disturbing!

 

[Woodnaut]

Re: Transom height and motor??

I'll throw this out there for what it's worth, even though it might be unrelated since it's a totally different horsepower range.

I had a four blade 18" pitch prop on my 90HP outboard. The engine was barely hitting 5,100 RPM at WOT. I had the prop repitched to 17" and the RPM came up to around 5,800 RPM. However, prop slippage was definitely occurring when trying to get up on a plane. Once up and moving, the slippage stopped and the engine could be heard to clearly load up. I had some cup put into the prop and the problem went away.

Could the slippage (over-reving) you notice be due to a slightly "under-pitched" situation? This is to say, maybe you need to load the engine up a little more with a little more pitch. (Of course WOT on your engine needs to be within the mfg's recommendations.) Also, do smaller props have hubs that can be "spun" like larger props?

 

[dew2]

Re: Transom height and motor??

Thanks for replying; Yes the smaller props can be spun,This 15 HP was put on another 14ft boat and works excellent.

 

[fisherguy123]

Re: Transom height and motor??

I had the same problem with a 14` open fiberglass runabout. It was very heavy , about 500pds: me 240 pds, passenger 150 pds ; gas 50pds; motor about 120pds. Had a 9" pitch prop and couldn`t get over 35kms per hour out of it and drank gas like V8. A big roller wake was behind boat a 1/2 throttle.
Reved up like screaming banshee. Changed to a 11' pitch and all my troubles went away, clocked on a GPS with same load and she skimmed along at 43kms per hour. Then stuck 3/4 piece of hockey stick under the motor to raise it{ same brand as Gretzy used I guess } and gained 2 more kms per hour. I never thought a prop could make such a difference !!!!