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

C

Colinesc

New member
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
 
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.
 
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.
 
Colinesc":m03j5k09 said:
The placard on the transom is rated for a 55hp, but I often carry heavy loads and/or 5-6 people
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Steve makes a good point for staying with the maximum HP requirements for your vessel. What prop are you using? With consistent heavy loads, a lower pitched prop to keep the motor in the higher recommended rpm range may be helpful and better for the motor.
 
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.
 
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.
 
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.
 
The sticker for boats under 20' takes many factors into account
Click to expand...

so what is the formula for figureing out Hp rating? I mean ever cdory is based on a design that was made for a 70hp motor. Now many are powered with 90s and 115hp. Very little has been changed in the design. Nothing at the transom other then the amount of v or more to the point less of a lack of a v. We are not talkig about hanging a 225 hp motor on a boat that came with a 150, hang on a minute???
 
(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....
 
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.
 
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