Max HP For StarCraft Mariner

[Dougb616]

Looking for some advice on the size of an outboard to install on a 22 foot 1978 StarCraft Mariner. I was recently told that the transom on this craft can only handle a certain weight with the the forces exerted. I was looking to buy an outboard with a HP rating of 175 to 200.
I am going to replace the wood in the transom with Coosa board and also replace the aluminum transom due to extreme pitting.

 

[Willyclay]

Welcome to the forum! The members here are great and can help you with any issues involving your boat, motor & trailer. My old geezer brain thinks your 22ft boat falls outside the criteria (20ft) used by USCG for commercial boatbuilders but you can probably use their formula to calculate the maximum horsepower that would be reasonable. Anything greater than that amount may put you in "lawyer-land" if insurance companies and/or third-parties are involved in an incident. Be safe and good luck with your project!
EDIT: Link to USCG regs.:

https://uscgboating.org/regulations/assets/builders-handbook/SAFELOADING.pdf

 

[lprizman]

Always max out HP!

Welcome!!!

 

[jbcurt00]

Your 1978 should be rated at about the same as a 1979 Mariner, 240hp....

If you are considering a 4cycle 200hp motor weight may be a factor, but a 2cycle 175-200hp should present no problem.

Its originally an outboard 22ft Mariner, not a remuddled other model, correct?

If so, a 200hp OB should be fine.

Good luck w your project.

 

[Dougb616]

Your 1978 should be rated at about the same as a 1979 Mariner, 240hp....

If you are considering a 4cycle 200hp motor weight may be a factor, but a 2cycle 175-200hp should present no problem.

Its originally an outboard 22ft Mariner, not a remuddled other model, correct?

If so, a 200hp OB should be fine.

Good luck w your project.

This is an original outboard 22 ft mariner. Do you think that should add knee braces to the transom to be safe?

 

[jbcurt00]

If the boat, hull, transom, transom knees, end caps, splashwell and rivets are all sound, no, no need for it.

The transom was designed as part of a system (knees, plywood, splashwell & etc).

When 'overbuilt is better' guys tear into a boat and make changes and additions, stress gets transferred from where it should have been countered to other areas of the system or other places that werent intended to carry that stress.

I'm not a naval engineer, but I slept pretty good last nite in an apartment near a Holiday Inn Express, so........

Just my $0.02

 

[Dougb616]

If the boat, hull, transom, transom knees, end caps, splashwell and rivets are all sound, no, no need for it.

The transom was designed as part of a system (knees, plywood, splashwell & etc).

When 'overbuilt is better' guys tear into a boat and make changes and additions, stress gets transferred from where it should have been countered to other areas of the system or other places that werent intended to carry that stress.

I'm not a naval engineer, but I slept pretty good last nite in an apartment near a Holiday Inn Express, so........

Just my $0.02

Thank you for the information. Everything you said makes perfect sense. I was concerned about installing an outboard over 150 HP because someone stated that I should not go that big due to flex in the transom with weight and the overall force of the motor during take off getting on plane. I am hoping to get close to a 200 HP outboard but just want to make sure the transom can handle the weight and forces exerted on the transom when running.

 

[jbcurt00]

2cycle or 4cycle 200hp?

I might tend to shy away from a 4cycle that big, but ratings are complicated these days. I suppose in theory a 200bp could possibly weigh about the same if it shares a block w a 175hp outboard.

None of my motors have ever been that big nor as new as you're likely to buy, I am completely unfamiliar w 4cycle outboards

 

[matt167]

If that boat were an I/O Starcraft would have shipped it with either 140hp 4cyl or 165hp 6cyl.

I think anything north of 140hp will be fine

 

[rtek816]

I have a 1986. Placard rates max HP as 140. FYI