Transom Height

[Cabbitt]

Hello all. I've done a search, and read a lot (great site!) and I have a question. I have an old 14' aluminum that I hung a 1996/9.9 Mercury 2-stroke on. I injured my back and have to upgrade to an electric start motor ? (I'm looking at a 15 HP Yammy 4-stroke). I'm a bit confused about transom height, though.
The boat transom appears to be 16?. The shaft on the 9.9 is 18?. The new Yammy comes in 15? (short) and 20? (Long). Assuming that I need the longer shaft, will I need to shim the top of the transom to bring the plate/prop to where they should be, or will racking the motor out work? I've posted a couple of pics of the current setup.

Thanks,

Bob

 

[metriccrescentwrench]

Re: Transom Height

I don't know what you mean by "racking the motor out".

When it's said that a boat has a certain size transom that's referring to the vertical measurement from the top of the transom to the bottom of the boat when the boat is sitting level (not the measurement of the transom itself - remember your Pythagorean Theorem), so it sounds like your boat has a 15 inch transom.

And from that photo it looks like the engine is sitting lower than it needs to be.

 

[pckeen]

Re: Transom Height

Hi Cabitt,

Welcome to iboats. Although motors come in 15 (SS), 20 (LS), 25 (XLS) and 30 inch shaft sizes, boat transoms don't. A 16 inch transom would fit a short shaft, and isn't unusual. See the attached link for some additional information.

 

[Cabbitt]

Re: Transom Height

Thanks for the responses. So, I should be OK with the short shaft 15 (15") motor, right?


Regards,

Bob

 

[Frank Acampora]

Re: Transom Height

It is WAY easier to raise the engine than to cut the transom! If you are buying from a dealer, let him test fit both size engines for you then buy the one that fits best. Otherwise, I would go with the long shaft and raise the transom a bit. It is not a difficult job and there are numerous posts on the forum about people who have done just that.

And BTW: Just like transoms, shaft length is advertised as 15 or 20. That may or may not be the real length measurement

 

[Texasmark]

Re: Transom Height

If you go to www.oldomc.de and look at the sales brochures on there you will see all sorts of engine heights vs transoms. Back then there seemed to be no standard. The 15" engine is made for a 15" transom, give or take. On a 10 hp engine you aren't really going to notice the difference if it is lower in the water or not. Other thing is the alum boat has a center extrusion where a keel would be and it can cause turbulence which could effect performance in turns tight turns at high speed. But you aren't going to get high speeds with a 10 hp engine on a 14' alum boat. BTDT

There are probably 10 million small boats out there with another 10 million outboards hanging on them. The boats are from 10,000 manufacturers and the engines from a hundred. They all seem to get along together somehow and have for the last half century.

Buy your engine and be on your way. However, a word of caution on that brand of engine. We just went through a big problem on another site with a guy who bought an old Mariner which he said was a Yammie with a Mariner paint job; aka Mariner engine built by Yamaha. He was looking at having to pay $50 for a thermostat for it where Merc stats for similar hp engines, and for my Merc. were $10 on this site. You might look into the cost of ownership. Gave me a wake up call as I was going to replace my 90 Hp Merc. with a 115 V4 Yammie and now forget it.

My 2c,
Mark