Why is this motor so long?

[jktrahan]

I built my own boat. According to plans, the transom was cut to be 15" tall, which made since because I thought a short shaft motor was 15" measuring from the place were the motor rest on the top of the transom down to the top of the cavitaion plate. <br /><br />Well I did not have a motor when building the boat. I picked up a little 9.5 Evinrude "short shaft" and put it on my boat thinking everything was fine. When I tried it out on the water the bow was still high after getting on plane and the back seemed to be to far into the water, so I added a Doel-fin. Did not help?<br /><br />After reading the post on this forum I realized my cavitation plate was to low in the water. I measured the motor and it's 18". Does this sound right or has something been added to this motor? I'd like to raise the motor, but i'm out of transom now? Any Ideas.<br /><br />I'm trying to add pics below:<br /><br />

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<br /><br />This is a 1967 9.5 Evinrude.<br /><br />Thanks for any advice <br />More Pics of Construction[/http]

 

[JB]

Re: Why is this motor so long?

Hi, Joey.<br /><br />Sharp looking boat!<br /><br />Check your model number. If it has an "L" in it you got hosed, it is a long shaft engine.<br /><br />You don't seem to have much angle in your transom, but this might contribute. The 15" measurement should be vertical, not on the transom surface.<br /><br />Give us your model number so we can verify that your engine is really a short shaft engine.<br /><br />Take the Doel-Fin off until you can get the AV plate at or slightly above keel level. In your current situation it will pull the stern down, not lift it.<br /><br />Let us know.

 

[jktrahan]

Re: Why is this motor so long?

Thanks JB, the transom does have a small angle, about 5 degrees or so.<br /><br />Here's the S/N MQ-13M and the Model: J2728701

 

[roscoe]

Re: Why is this motor so long?

My new 4hp Merc has a 17" shaft also, even tho the model is listed as a short shaft.

 

[KenOhki]

Re: Why is this motor so long?

I took a real close look at your pictures. Looks to me like you need too raise the motor about 3, maybe 4 inches. The Anticavitation plate should be within 1 inch of the bottom of the boat as a general rule, looks like you are 3 maybe as much as 5 inches too low, hard to gauge that from a picture. I have a fiberglass boat, and needed to raise the transom 6 inches to occomadate a long shaft motor, I used a piece of presure treated 2x8 and some heavey dutey C clamps to mount my motor at the right hight ( had to be removable to use other motor too ) You have a wooden boat dude, Just add a board like I did, Only you can bolt it right through the transom. The way I did it is rock solid with the clamps, But for a permanant install, I would bolt it. <br /><br />Nice job building your boat. I am concidering doing one myself. here is my boat, and what I did.<br /><br />

 

[jktrahan]

Re: Why is this motor so long?

OK, I lifted the motor with a 2x12 and the cavitation plate is about even with the bottom of the boat. Tried it out with and without the Doel-Fins. Still the same results.<br /><br />The motor will "plane", somewhat with just me (200lbs) in the boat + 6 gal gas tank around the middle of the boat. But if I had a 100 lb child, the boat will not plane. Even if they sit on the front deck.<br /><br />I now think the problem is the motor is not reaching the prober RPMs and not pushing with as much power as it should be. At WOT, the motor sounds like a loud hmmmmmmm, but at a much lower pitch sound than I excpect an outboard on plane to sound (High pitch whiiiiin).<br /><br />I pulled the spark plug cables one at a time to make sure both cylinders were hitting and they both are. I checked my plugs and they looked balckish and slightly damp, which is ok, I think. Also checked the plug gap @ .30 and it's ok.<br /><br />I'm thinking of getting a carburater kit and cleaning the carb good then decarbing the motor.<br /><br />

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<br /><br />I should also mention, that the motor runs ok except for the lack of power and a little rough idle after running wot.<br /><br />The boat is very light, less than 150 pounds.<br /><br />Any other thoughts??

 

[jktrahan]

Re: Why is this motor so long?

Motor also starts on the first crank, and pee's ok.<br /><br />Thanks again for any advice..

 

[jktrahan]

Re: Why is this motor so long?

Prop is 8 1/2 x 8. Sorry, but I know someone is going to ask, and I want to give u all the facts up front.

 

[jktrahan]

Re: Why is this motor so long?

Prop is 8 1/2 x 8. Sorry, but I know someone is going to ask, and I want to give u all the facts up front.

 

[Chinewalker]

Re: Why is this motor so long?

Hi Joey,<br /> I'd guess that your boat isn't meant to plane off in the traditional sense, as it appears to be somewhat of a displacement hull. Long and narrow boats sometimes don't have enough planing surface to accomplish the job with modest power. If you were to add a 15hp motor I think you'd find the boat a little squirrely on plane. The problem appears to be in the design...<br />- Scott

 

[jktrahan]

Re: Why is this motor so long?

There may be something to that... The boat is 41" in the middle and around 36" or 37" at the stern.<br /><br />How can I test the motor to see if it's getting to 4500 RPM's. If I put a tiny tach on it and it's not planing, will my RPM's be lower because of this?<br /><br />Thanks

 

[Chinewalker]

Re: Why is this motor so long?

It takes more effort to push a boat through the water than it does to push it over the water, so, yes, your RPMs would climb a bit if the boat gets over the hump. This is why the same throttle settings result in different RPMs when you're planing off a boat alone vs. when you're trying to get a skier out of the water...<br />- Scott

 

[jktrahan]

Re: Why is this motor so long?

That makes sense. I think before i do anything to the engine, I'll get a tach and one of those 3 foot arm extenders that allows me to move further to the front of the boat and check out what the tach reads.<br /><br />Thanks again.