big twin shaft length/transom height?

[pcrussell50]

1959 super seahorse, 35hp, rds21b...

it is mounted on my 13.5', 1960 span america with a 15" transom. see this photo

i wonder if this motor is really a smidge too tall for the transom height? i'm only guessing this based on the fact that the cavitation plate appears to be about 2" lower than the bottom of the transom. but i guess i'm not sure what the ideal should be. and this motor is not the tall shaft version, even though it looks pretty tall to me. the tall shaft version is the rdsl21, with the "l" after the "rds"

anyway, i was just wondering if this situation is sub-optimal or if it's really just about right.

for grins, i'm going to try, [yet again] to inline link the photo directly into the post here below:

-peter

 

[CATransplant]

Re: big twin shaft length/transom height?

Those old timers run a little deeper than modern motors. You look OK to me, there. If my memory serves, from the transom mount to the anti-ventilation plate, those engines are 17". The extra couple of inches keeps the waterpump below the water level.

Some guys do block these up on the transom on a 2x2 (1.5x1.5). That still leaves plenty for the transom screws to grab the transom. It raises the outboard 1.5". As long as the water is coming out the exhaust relief hole halfway up the leg, you're OK.

You can experiment to see if you can raise yours. If the 1.5" is too much, try 3/4".

 

[CATransplant]

Re: big twin shaft length/transom height?

Oh, yeah...one more thing: Those are sweet outboards. My 1958 RDS20 was my favorite outboard of all time. Always started up instantly, and pushed my 14.6' trihull about 26 mph with no strain, and would slow down to a lovely burble for trolling.

Take good care of it!

 

[Chinewalker]

Re: big twin shaft length/transom height?

I have run a Big Twin short shaft as high as 19-1/2 inches in a racing set-up. Not likely to work that high in most applications, though...
- Scott

 

[CATransplant]

Re: big twin shaft length/transom height?

I'm betting that 13.5' boat was designed with the Big Twin in mind. A lot of boats around 1960 were, and it's too small for a Fat Fifty. I expect that the OP is going to be very pleased with its performance once he gets out on the water.

We've come so far with our boats since then that a lot of people are surprised at what a boat designed for about 35-40 hp will do. A whole generation learned to waterski behind boats just like that. The boats were lighter in weight and built to do really well with the engines of their day.

Seems to me that, in these days of uncertain fuel prices, there might just be something in stepping back to the designs that will perform well as family boats with outboards between 25 and 50 hp.

But I'm an old codger, so what do I know?

 

[pcrussell50]

Re: big twin shaft length/transom height?

I'm betting that 13.5' boat was designed with the Big Twin in mind. A lot of boats around 1960 were, and it's too small for a Fat Fifty. I expect that the OP is going to be very pleased with its performance once he gets out on the water.

But I'm an old codger, so what do I know?

CAT, I've actually had the boat since last june of '08, and i'm certainly pleased with it. it gets up and planes with the wife and me and our gear. it's not exactly a chine-walking, bow-lifting, "skipping off the pad", type of plane like my 16' sportster with a 135, but we use it for running about in the ocean, and fishing and picknicking on sandspits, or my friends and i use it for towing each other on surfboards, [slow, nose-high], not planing.

still, i'll forever be tempted to put a light 50 on it, like a 2-stroke merc, [if the nada weight guide is correct, it's not much heavier than] the 35hp johnnyrude.]

but man, i do love this old mill. i like that it's simple, and responds to my tuning efforts. and i _really_ like that it's 50 years old and not a show queen. it's a workhorse with faded paint, and greasy fingerprints, that earns its keep by propelling our boat, not winning show trophies at aomci shows, [not that that would be bad, either ], that doesn't give up anything to the newer machines, except for the faded paint and greasy fingerprints. so yes, i gush over it, and i'm not even a codger yet and when i am, i have every reason to believe this old gal will still be going strong.

btw, it's "fully optioned" with electric start and generator, but the previous owner had removed the voltage regulator. so i removed the generator drive belt, because it's in good shape and i hear they are expensive and hard to find, so i didn't want to waste it until i get a new VR installed and ready to run.

-peter