HP Ratings for Twin Outboards vs. Single

[trendsetter240]

I've noticed when looking at new boat dealer websites that frequently there are different HP ratings for twin outboard setups vs. the single outboard setup. Same boat but different max HP depending upon the number of outboards bolted to the back.

An example is the Campion Allante:

Campion 822 Sport Cabin Bracket & 822i Sport Cabin. 350hp Single or 600hp twins.

Now this is a large boat (30ft) but does the same principle apply to smaller boats as well?

Reason I ask is I have a 1969ish Slickcraft SS170v which has no rating plate and comes up with a max of 115HP using the coast guard formula.

It just so happens that I have twin rebuilt 1995 evinrude 70hp outboards now. I'm wondering if there is another formula used for the twin setup. Information on this for my specific boat is not available anywhere.

What do you guys think?

 

[diesel5599]

Re: HP Ratings for Twin Outboards vs. Single

More than likely due to the way that particular boat is built, its transom can only handle 350HP within the square footage of a single transom bracket or 600HP overall for the entire transom.

However I would definitely not use that one boat to make a decision like you are facing. No two boats are alike. My Century 2400 has the same rating (300HP max) for either a single or for twins.

 

[trendsetter240]

Re: HP Ratings for Twin Outboards vs. Single

More than likely due to the way that particular boat is built, its transom can only handle 350HP within the square footage of a single transom bracket or 600HP overall for the entire transom.

However I would definitely not use that one boat to make a decision like you are facing. No two boats are alike. My Century 2400 has the same rating (300HP max) for either a single or for twins.

Thanks for your reply, I most likely will not pursue putting the twins on my current boat. Weight tests out fine but there is not enough clearance in the splash well to get them far enough apart.

I'm still interested in why they might make the ratings different for twins in some cases...

 

[Bob's Garage]

Re: HP Ratings for Twin Outboards vs. Single

More than likely due to the way that particular boat is built, its transom can only handle 350HP within the square footage of a single transom bracket or 600HP overall for the entire transom.

However I would definitely not use that one boat to make a decision like you are facing. No two boats are alike. My Century 2400 has the same rating (300HP max) for either a single or for twins.

This sounds very plausible. I have never noticed a difference between single and twin ratings before. Could it also have something to do with there not being a 600hp single engine available? So the maximum single is the max available at the time, but the maximum actual hp rating is 600 hp? Maybe a definitive answer could be determined by asking them?

 

[QC]

Re: HP Ratings for Twin Outboards vs. Single

Maybe it's because the max Single you can get is 350 . . . Just sayin'