Determining Max Outboard Engine Size

[jdawwggin25]

I wanted to know what actually determines the max engine hp rating for certain boats. I have been going through the old pamphlet for my 87 Aquasport 200 Osprey as well as different engine specs for the yamaha outboards. The 200 osprey has a max hp rating at 185 but the 222 osprey has a rating at 235 hp. The design is the same, 40 more gallons in the fuel tank, and weighs about 300 extra pounds.

Second question is that I have a 87 yamaha 115 2 stroke and an option to switch to an 89 yamaha 235 excel micro comp outboard. If I do so will I have to make modifications to the boat at all or should I be okay to switch?

Thanks for the help.

 

[Silvertip]

Re: Determining Max Outboard Engine Size

This question is asked time and time again and the answer is always the same. The boat manufacturer indicates a maximum HP rating on the capacity plate in the boat. That maximum is based on the design of the boat and is there for your safety and the safety of everyone else that shares the water with you. You are proposing overpowering by 50 HP. Your insurance company may not like you should you ever be involved in an incident -- your fault or not. Your passengers (or their attorney) would go after you like flies on stink regardless how friendly you think they are. Boats over a certain size do no have a maximum HP rating. The 22 footer is 3 feet longer than the 18 so it can very likely handle the extra power. You really don't have a good motor for the boat. A 115 is really too small if you consider 75% of max rated HP as the guide for "minimum" acceptable HP. A 150 - 175 would be ideal (and safe).

 

[Texasmark]

Re: Determining Max Outboard Engine Size

Might google BIA boat rating or something of the sort and get your answer. It has to do with several things including length and transom width. On the insurance and engine size you can bet your bippie they are interested in what you are running. Your engine size vs rating is a box on the application; with State Farm anyway.

Mark

 

[Jlawsen]

Re: Determining Max Outboard Engine Size

It would be very difficult to determine exactly how the manufacturer of your boat finalized the maximum hp rating. You would need to know the exact design specifications and the results of all the testing that ulimately produced a boat that met or exceeded all the safety regulations of multiple agencies. I believe that it would suffice to say that the max hp rating is cut in stone once it's permanently assinged to the boat. Like everyone say's once it's assigned, your biggest risk is liability should you choose to ignore the rating.

The proof is in the fact that you can build your own boat from a set of plans (or not) and power it as you wish. There are very few restrictions or requiments beyond basic saftey that you must meet. It can be a 2x4 with windmill power as long as it does not endager you, your passengers or others in the vicinty of operation. The USCG does have specific instructions for what they would like to see home builders do and there are a lot of "must" statements in it but the choices are so varied that it is impossible to enforce them. The hydrofoil and the submarine would not be buildable privately if they could.

That may not specifically answer your question but it may give you a better understanding.

 

[jdawwggin25]

Re: Determining Max Outboard Engine Size

I fully understand the insurance issue on this topic. What we are looking to do is a complete overhaul on the 20' center console. We are pulling up the deck and adding extra support to the stringers and tying them into the transom that we are rebuilding. We plan on closing in the transom and adding a foot of storage space and extra bracing. We are building a transom bracket with swim platform that is rated at 300 hp. With all the additional support and flotation foam added we should be fine to handle a 225hp outboard.

My only wonder (besides the insurance) is if we do all these modifications should we be okay to support the 225hp motor. Trucks I have a better understanding of and we have modified a 4runner to hold a 460 big block and it just took adding the extra support in the right spaces. The 225hp is 7#'s heavier than the 185hp motor that is the max rating so I feel that weight is not to much of a worry. Im thinking that its going to be the power and torque of the engine. In your opinion would these modifications support the 225 without worry. Again taking insurance out of the equation and the only reason for the 225 is because that is the only available option to me right now. I cannot find any 150-185hp motors in my price range. Thanks for any help, sorry if this post comes across arrogant or rude, I do not mean it that way.

I do appreciate the insurance info and I will be contacting them this week as well.

 

[coastalrichard]

Re: Determining Max Outboard Engine Size

jdawwggin, your boat is 20', therefore no HP rating applies

? 183.51 Applicability.
This subpart applies to monohull
boats less than 20 feet in length, except
sailboats, canoes, kayaks, and inflatable
boats, that are designed or intended
to use one or more outboard
motors for propulsion

 

[jdawwggin25]

Re: Determining Max Outboard Engine Size

Appreciate the info. I also talked with my insurance agent and he said that it is okay just to let them know the engine model so that they can change it on the plan.

 

[Bob_VT]

Re: Determining Max Outboard Engine Size

jdawwggin, your boat is 20', therefore no HP rating applies

? 183.51 Applicability.
This subpart applies to monohull
boats less than 20 feet in length, except
sailboats, canoes, kayaks, and inflatable
boats, that are designed or intended
to use one or more outboard
motors for propulsion

You should re-check the regulations http://www.uscgboating.org/regulations/boatbuilder_s_handbook/downloads.aspx

The horsepower rating applies. Not trying to sharpshoot however....... the correct answer's are in the book.

 

[coastalrichard]

Re: Determining Max Outboard Engine Size

I scoured them Bob and I found it confusing. The regs say one thing one place (as I posted) and then seem to contradict that by saying that the motor cannot exceed manufacturers plated rating. So what's the definitive answer....20'+ with a plate is the maximum or no maximum if 20'+ and not plated???????? Obviously, you have way more experience than I

 

[Jlawsen]

Re: Determining Max Outboard Engine Size

jdawwggin, your boat is 20', therefore no HP rating applies

I thought the rule was 20' and under. I must have missunderstood.