# 15' with 90?



## DuckNut (Apr 3, 2009)

Please loosen your mask


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## 321nole (Jan 11, 2016)

I say tighten your mask, you don't want it flying off when you're doing 60mph across the lake.


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## Tony P. (Apr 24, 2019)

DuckNut said:


> Please loosen your mask


so bad idea thanks for the info but what would you recommend max hp to be on that kind of boat? cg rated it max 25 but im going to be adding alot more weight so i have no clue what hp to get. any info would be greatly appreciated


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## DuckNut (Apr 3, 2009)

You are going to have to use the CG formula but adding stuff into it won't increase the hp rating.


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## Tony P. (Apr 24, 2019)

DuckNut said:


> You are going to have to use the CG formula but adding stuff into it won't increase the hp rating.


well i was hoping to get a little speed but i guess this will have to just be a fishing skiff thanks for your reply


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## ceejkay (May 7, 2016)

i wouldn’t advise it. It’s rated for 25hp. Lot of variables but I’m gonna say that’s because of weight. Cg considers a “person” 150 lbs. It was probably designed for 2 people in the back, 5 gal gas tank, 25hp, somewhere in the neighborhood of 550lbs in the back of the boat. Don’t know the displacement of the hull, but if I was going to guess I would say somewhere around 700 lbs on the back of the boat will be real close to swamping over the transom at rest. Just my .02$ on the subject, and I could be way off base here


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## LowHydrogen (Dec 31, 2015)

You can do it because you can do anything.

Make sure the sponsons are big, and I would have them built so the bottom is actually a planing surface this will help you with the chine walking (it will). You're going to want 6-8" setback, jackplate, a 24p (minimum) stern lift prop if you really want it to air out, and larger underwear to house the balls it'll take to open it up.


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## mro (Jan 24, 2018)

I'm on my third Sea Nymph, a seventeen footer.
In their day the nymphs were a well made aluminum boat for a riveted hull.

Putting a 90 hp on that model I'd think would be a real risk of ripping out the transom if it didn't sink upon it's maiden launch.


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## Tony P. (Apr 24, 2019)

mro said:


> I'm on my third Sea Nymph, a seventeen footer.
> In their day the nymphs were a well made aluminum boat for a riveted hull.
> 
> Putting a 90 hp on that model I'd think would be a real risk of ripping out the transom if it didn't sink upon it's maiden launch.


i was going to modify the transom heavily lift it to 20", 2 in thick, jackplate, pods, ect... the reason i was wanting a higher hp is because my dad about 15 years ago had a 15 foot side console aluminum that had one of the old 15 in shaft Evinrude 40 hp and i was thinking because i was going to be adding a lot more weight to the bow i would need/ want a lot more power i was hoping to get 40-50 mph but as Ducknut said its probably a very stupid and dangerous idea i am not very knowledgeable on the subject of heavily over powered boats that is why i was asking for suggestions


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## Tony P. (Apr 24, 2019)

thanks to every one for their input on this post! they where all extremely helpful thank you


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## JC Designs (Apr 5, 2020)

Sounds like a higher hp fliver to me! I say do it!


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## mro (Jan 24, 2018)

Vibration fatigue

In the eighties I had a hydraulic trailer i bought for my company which the bed could be lowered to the ground and small vehicles could be driven on, then the hydraulic system would raise it back up for towing.

The fenders were a constant problem. Every few months I had to repair them so they wouldn't fall off.

I redesigned them and made them from 1/8" steel plate, welded and reinforced. I was pleased that they were so strong that I could stand on them (me at the time 180 pounds) and they didn't even flex.
They became a solid part of the trailer (so I thought).

Long story short, I'm towing the trailer with a 4,000 pound machine in it on the interstate and the left fender just falls off.

What happened (according to an engineer) the fender was vibrating at a frequency which may have reinforced the vibrations and the steel broke.

I replaced the transom on my nymph. Think I did a good job and think it is stronger now than when it was new. That being said I will be inspecting it regularly during the first few trips and after for a year or so. The boat is rated for eighty-five HP and I put a 60 on it.

Expect to be on the water next month.


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