Revised Transom Strength Motor size

[yoda5195]

I'm in process of moving a 1982 70HP Evinrude from a 16" Crestliner vintage 70's to a 17" 1968 Glasply, replacing a 1980 40 HP suzuki. The glasply is in good shape, constantly garaged, no gelcoat cracks or issues. A well meaning friend interjected that the older boat was not meant to hold that much HP or weight. both boats have 2' wide transom, both are 20 inch deep transoms.... I don't think it's a problem. give me your feed back.<br /><br />thanks!!

 

[DJ]

Re: Revised Transom Strength Motor size

edited.

 

[quantumleap]

Re: Revised Transom Strength Motor size

Actually you didn't give him an opinion at all. You just argued the definition of 'short shaft'. On larger motors short shaft is 20" and long is 25". I assume that was his reference point. He is asking if that motor is too much HP for his boat. He obviously re-posted to try clarify the length of the motor.<br /> Tide-Man, Welcome to the site! You can edit your first post without having to post again. Your boat may be too old to have a capacity plate, so do a search on this site using the red 'Search' icon above for "coast guard hp rating formula" or something along that line and you can figure out if it is mathematically safe. Keep posting if you need more help as most people here are very helpful and friendly.

 

[Scaaty]

Re: Revised Transom Strength Motor size

A lot of people get confused on shaft size DJ, and if both motors are the same shaft size, it doesn't matter as that is not the question Tide-Man asked. Anyway, I just sold (co-sign) my neighbors 1967 Fiberform that had a similar year 70 hp Evinrude that he took fishing out of Puget Sound (Edmonds), so I see no problem. If you want extra protection add some transom eyebolts, cable and turnbuckles, and a solid eyebolt mount in the boat rear somewhere.

 

[DJ]

Re: Revised Transom Strength Motor size

If the engine "looks" too big, and you do not have a cap. plate, one can expect to be ticketed. Regardless of what is said here.

 

[Scaaty]

Re: Revised Transom Strength Motor size

Forgot to say make those eyebolts and etc. stainless steel! Available at Loews. H-D.

 

[quantumleap]

Re: Revised Transom Strength Motor size

I don't think a 70 hp is going to look out of place on a 17ft, 20" transom boat. There are many 17 footers rated for much bigger motors than that. If it fits into the CG formula, you should be alright. In my state and a few others, if the boat was not manufactured with a plate, then the boat is posted with an "OR" in place of the capacity rating, meaning it is the owners responsiblity to power accordingly and to be liable if the boat is overpowered or overloaded.

 

[DJ]

Re: Revised Transom Strength Motor size

My Sport Canoe is 17' with a 20" transom. It's rated for a 6.<br /><br />Anyway, without coming across as a know it all, I just have a hard time telling someone it's going to be OK, without ever laying eyes on it.<br /><br />If you can, T-M, post a picture or a website where we can have a look. Then, I'll give a "guarded" opinion.

 

[quantumleap]

Re: Revised Transom Strength Motor size

Boat=apples, canoe=oranges. I think the beam between a canoe and a boat is a little different there DJ. The Coast Guard formula would reflect that difference.

 

[JB]

Re: Revised Transom Strength Motor size

Hmmm. a 24" (2') wide transom spooks me. That is about the width of a 17' to 19' square stern canoe. The boat must be very narrow and therefore not good for very much HP. Unless, of course, the 2' figure is in error.<br /><br />All of the relevant discussion here is about the physical characteristics of the boat that would determine a safe hp rating according to the USCG.<br /><br />A 20" deep transom takes a long shaft (20") engine. The 25" shaft is Extra Long (XL), and 30" is XX-long. The USCG formula takes transom depth, as well as transom width and beam, into account.<br /><br />Your answer is in how the measurements of the boat fit into the USCG formula, Tide-Man. Not in any of our opinions.<br /><br />Good luck.

 

[sorrydog]

Re: Revised Transom Strength Motor size

The USCG formula takes transom depth, as well as transom width and beam, into account.

But not hull design, intended use, or handling characteristics.<br />An Allison drag boat is rated at like 135. 95% of them are probably rigged with 200 or better.<br /><br />Anyway, when he said 2' wide transom, he was probably talking about the splashwell width.