2001 OUTRAGE 21 Re-power with Twin HONDA 90

Optimizing the performance of Boston Whaler boats
jklaiber1
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Joined: Wed Oct 12, 2016 1:08 pm

2001 OUTRAGE 21 Re-power with Twin HONDA 90

Postby jklaiber1 » Wed Oct 12, 2016 1:20 pm

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.

flymo
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Re: 21 Outrage Repower

Postby flymo » Wed Oct 12, 2016 3:56 pm

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
Last edited by flymo on Thu Oct 13, 2016 10:26 am, edited 2 times in total.

jimh
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Re: 2001 OUTRAGE 21 Re-power with Twin HONDA 90

Postby jimh » Wed Oct 12, 2016 8:34 pm

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.

porthole
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Re: 2001 OUTRAGE 21 Re-power with Twin HONDA 90

Postby porthole » Sat Oct 15, 2016 10:47 am

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?
Thanks,
Duane
2016 World Cat 230DC
1999 Outrage 21, Yamaha SW Series II 200
1997 Outrage 18, Yamaha 125
1983 15 SS, Honda 50
1980 42 Post
1983 34 Luhrs 340 SF

flymo
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Re: 2001 OUTRAGE 21 Re-power with Twin HONDA 90

Postby flymo » Mon Oct 17, 2016 3:45 pm

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.

jimh
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Re: 2001 OUTRAGE 21 Re-power with Twin HONDA 90

Postby jimh » Mon Oct 17, 2016 5:51 pm

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