CONTINUOUSWAVE

Can [a 2001 Boston Whaler OUTRAGE 21] take twin motors?

[If the twin engines were 90-HP] would [a 2001 Boston Whaler OUTRAGE 21] be under powered?

[Has] anyone done something similar?

[Give me your] thoughts or comments; they will be appreciated. Thanks


BACKSTORY: I [may buy an] 21 Outrage. I really want something with a [four-stroke-power-cycle outboard engine]. Every [used boat] I look at is much newer and more money then I want to spend. I have found a 2001 Boston Whaler OUTRAGE 21 with a 225 Optimax. I am thinking of buying it and then re-powering to four-stroke-power-cycle engines using YAMAHA twin 90-HP engines.

I'm not sure how that math is going to work out for you.

From a quick look around, a 2001 Outrage 21 goes for between $15,000 and $20,000. If you add $20,000 worth of Yamahas you get to between $35,000 and $40,000 - and Hondas would be even more. Are you sure you can't buy a newer Boston Whaler boat with the motor you want for that kind of money? Re-powering an older hull is rarely worth it, financially.

Regarding repowering with twin 90-HP engines: those will give you about the same performance as a single 150, but cost more and use more gas. If the boat is rated for 225, I'd be concerned about powering it with what's effectively 150-horsepower.

Flymo

The use of twin engines on outboard-powered boats is somewhat controversial when the total horsepower of the twins is less than 400-HP. These days, with modern single engines available in 300-HP models, there are few twin engine installations with engines of less than 200-HP each.

You should look for some literature from Boston Whaler about the performance of a c.2001 OUTRAGE 21 to get an idea of what sort of boat speed will come from 180-HP. As FLYMO mentions, two 90-HP engine are probably not equal to 180-HP.

You mention that there is a limit to the amount of money you want to spend. What is the limit? It must be fairly high, as the cost of buying a used single engine boat and then immediately re-powering it with new twin engines of a different brand that originally rigged is going to be enormous.

The rule of thumb we always used for inboard boats was that a single engine was about 20% more efficient then twins of the same horsepower, meaning you could opt for 20% less power on the single to equal the performance of twins.

Example - twin 400HP diesels yielding 800HP total could be replaced by a single diesel of 600-650HP.

Does this hold true with outboards as well?

My guess of two 90-HP engine equally one 150-HP was just that, a guess based on performance I have seen reported. However, it roughly matches your 20-percent figure.

flymo wrote:My guess of two 90-HP engine equally one 150-HP was just that, a guess based on performance I have seen reported. However, it roughly matches your 20-percent figure.

If a single is considered to be 20-percent more efficient, then a single 150-HP is 1.2-times or 180-HP in twins. That's an exact match to the proposed 20-percent-more-efficient.

Let's see how that works for my boat: I have a single 225-HP engine. That suggests that twin engines would have to total 225 x 1.2 = 270-HP to get the same performance. Sounds like I'd need twin 135-HP engines. No thanks, I am very a happy with a single. Just finished my seventh season of perfect operation.

A simpler rule:

If re-powering to twins from a single engine, each twin engine should 0.6-times the horsepower of the single to sustain the same performance