Repowering 16' angler, thinking of yamaha 70 4-stroke

Colinesc

Im wanting to repower my 16' angler that currently has a 2 stroke Johnson 48 SPL (50 horsepower) and thinking about a yamaha 4 stroke 70. Has anyone done something similar? The placard on the transom is rated for a 55hp, but I often carry heavy loads and/or 5-6 people, and with the 48spl its pushing pretty hard to get up on plane. The yamaha 4 strokes use the same block for the 50, 60, and 70hp. They weigh 253lbs. The 48 SPL I currently have on it weighs 186 lbs. Seems like 60 more pounds wouldn't make much difference as far as stress on the transom. I spend the majority of my time on the Yukon and Tanana rivers, with less time in the ocean in south central Alaska.

Thanks in advance!

Colin

JT · Posted: Tue Sep 05, 2023 10:12 pm Post subject:

I can't say how it will do but I did see a 16' with a 70 horse here in Juneau last summer. I have a 45 Honda with a Yamaha 8 horse on the transom and no problem.

srbaum · Posted: Wed Sep 06, 2023 10:32 am Post subject:

Colin,
As a retired Coastie, I have seen several events in my time, that had negative consequences, because of powering above the factory certificate. In both cases, the insurance companies provided justification for settlement in the favor of the other party (not the boat owner).
Just putting this out there, for your consideration.

DayBreak

T.R. Bauer · Posted: Thu Sep 07, 2023 12:09 am Post subject:

Just throwing it out there....but your 50 hp 2 stroke might only have 50 hp at the powerhead and not the prop. The modern 4 stroke outboards are rated at the prop. This difference may very well be enough. As a side note....5-6 folks on a CD 22 is really cramped, I can't imagine a CD 16....yikes! It's your boat, your money, and your liability if you overpower it and the insurance company can prove (within reason) the accident was caused by an overpowering situation. As for what will really happen if you power it with a 70 hp? I don't know....nothing....something....there are plenty of 16 foot boats that have a sticker saying the max power is way more than that.

Colinesc · Posted: Wed Sep 20, 2023 1:48 pm Post subject:

Appreciate everyone's input! Happy to be apart of this community.

Colin

starcrafttom · Posted: Wed Sep 20, 2023 7:19 pm Post subject:

To me the sticker is about the weight of the motor not necessarily the HP. So if the 50 and 70 weight the same I would go wih the 70. better to use 50 hp of a 70 hp motor then to need more then 50 and not have it. Also get a bigger boat or fewer friends.

srbaum · Posted: Wed Sep 20, 2023 7:53 pm Post subject:

Thomas,
The sticker for boats under 20' takes many factors into account. Over time lessens (usually though casualties/deaths), causes new reviews and implementation of regulations as things change. Also fact of peoples weights have changed (upwards) and engine weights have also changed. So, more specifically the regulations can be found here 33 CFR 183.51-53.

Foggy · Posted: Thu Sep 21, 2023 8:09 am Post subject:

People do get into trouble.

I'll go with Mark Twain's reasoning.

starcrafttom · Posted: Thu Sep 21, 2023 4:39 pm Post subject:

srbaum · Posted: Thu Sep 21, 2023 5:01 pm Post subject:

Starcraftom,
This link will show you the formula that boat manufacturers must meet, for certification.
https://www.ecfr.gov/current/title-33/chapter-I/subchapter-S/part-183/subpart-D/section-183.53#:~:text=§%20183.53%20Horsepower%20capacity.,(b)%20of%20this%20section.

starcrafttom · Posted: Thu Sep 21, 2023 5:20 pm Post subject:

(3) Test conditions. The test must be conducted with no load other than a driver who must weigh no more than 200 pounds.

Well there goes my next career up in smoke....

Safetythird · Posted: Fri Sep 22, 2023 7:47 am Post subject:

Number of people that can be safely carried on a boat = (boat length X boat width)/15

So theoretically, 6 people is allowable, but that formula assumes everyone weighs 150 lbs.

You may be overloading your vessel in an unsafe manner.