HP recommendations for my 13' wood boat

[Mattgaw122]

I have a 1957 Thompson, 13' wood boat. I believe it is a sea coaster. What size HP should I be using with this boat? It had a 50hp Mercury on it before.
Any recommendations would be appreciated. I was told a 35hp was ideal

 

[Scott Danforth]

Use the us coast guard formula for hp. https://www.gpo.gov/fdsys/pkg/CFR-2002-title33-vol2/xml/CFR-2002-title33-vol2-sec183-53.xml

If your transome is over 20" high and assuming a 4-1/2' wide transom, I calculate 27hp

 

[Mattgaw122]

What do you recommend for a max horsepower? I'm looking at a 65 hp mercury to replace the 50 hp currently on it.

Any thoughts? Is that to big?

I also have access to a 40 hp motor also.

 

[jbcurt00]

65hp is way too much, IMO, but a 40 or 50 is too, based on the USCG calc method.

30-35hp would seem perfect

 

[Mattgaw122]

Thank you for the great information, I will look for a smaller outboard.