twin vs triple conversation over a beer or three

[the man]

so this isn't about money, efficiency, or even common sense- just a conversation that should involve us having beers while talking. I have a boat I am restoring, and will be re-powering with outboards. It used to have twin 351s & volvo outdrives in it, it will next have a bracket w/ flotation and outboards. The hull can handle a lot of power and some ugly conditions. Here is why am thinking triple 200s MIGHT be better than twin 300s:

- if one breaks, I still have two
- i could run on two, (lift the center one), and cruise slower OR put them all down for speed runs
- the boat would cruise at the same speed with less rpm on each engine
- 3 props is better than two (like bravo 3 or duoprop outdrives are better)
- it would look cool
- it gives me something for a conversation starter in port
- what the hell, why not?

so,how much of the above is total BS, and why would I do this or not do this?

 

[Streffpilot]

I really like the idea of outboard repowering. If it were me I would go with 4 strokes. Three two stroke motors can get LOUD at wot. But I think it's a good idea, but will be plenty expensive. I say go for it!

 

[UncleWillie]

If it matters.....
600 HP and dragging 2 Drives through the water is going to be more efficient than 600 HP and dragging 3 drives. Better MPG?
If you do not intend to use the center engine all the time, why drag around all that weight? (3 x 500lbs vs 2 x 600lbs)

 

[dingbat]

so,how much of the above is total BS,

Most of it.....given the reliability of today's outboards. KISS is a primary concern no matter how many HP you need hanging off the transom.

A vast majority of the on-water failures are fuel and maintenance related. Adding 30% to maintenance and higher fuel consumption only increases the probability of failure.

 

[Scott Danforth]

I would put twin 557's off the back if we are just talking over beers. Then again, depending on the boat and hull shape, I would probably keep it an I/O and just build up a pair of stroker BBC's with blowers

 

[Frank Acampora]

Why not go all the way and rig up like that drug-runner with 10 outboards? I mean, if you are talking beer balls, then everything is good--more is better and too much is best! Remember: Too much horsepower is never enough.

 

[Scott Danforth]

heck Frank, while we are at it, lets bolt a jet engine to it above the 10 outboards. that way it will make jumping a wake a whole new experience.

 

[the man]

Most of it.....given the reliability of today's outboards. KISS is a primary concern no matter how many HP you need hanging off the transom.

A vast majority of the on-water failures are fuel and maintenance related. Adding 30% to maintenance and higher fuel consumption only increases the probability of failure.

interesting... so adding a motor for extra redundancy increases the chance of one going out! most of what i have may be BS, but this logic is something that i have to digest a bit before i buy it. i do buy that 30% more maintenance plus the weight and drag is probably not the best choice.

thanks for the input. as far as the poster who said ' just rebuild the outdrives': 1. i want the space for storage in the boat 2. tired of u-joints going out and standing on my head doing "boat yoga" working on stuff 3. they are heavy 4. i want outboards

 

[dingbat]

interesting... so adding a motor for extra redundancy increases the chance of one going out! most of what i have may be BS, but this logic is something that i have to digest a bit before i buy it.

Simple probability.....2 is greater than 3

 

[H20Rat]

interesting... so adding a motor for extra redundancy increases the chance of one going out! most of what i have may be BS, but this logic is something that i have to digest a bit before i buy it. i do buy that 30% more maintenance plus the weight and drag is probably not the best choice.

Lets say that you have a 1 in 100 chance of having a motor fail in under 1000 hours. (made up numbers but possibly close to accurate) So with a single engine, your odds are simple, 1 in 100. Looking at it another way, If your trips are all exactly 1 hour, and you make 1000 of them, you have a .1% chance of engine failure each trip. A second engine means you have 2 in 100 odds of failing, or a .2% chance. Every engine you add just adds to your failure odds. 10 engines means a 1/10 odds of one dying before 100 hours, and a 1% chance.

 

[UncleWillie]

Iinteresting... so adding a motor for extra redundancy increases the chance of one going out! ... but this logic is something that i have to digest a bit before i buy it. ...

If there is 1:1000 odds of an engine failing per hour there is a 2:1000 chance that one of 2 engines will fail per hour.
However there is also a 1:1,000,000 (1000x1000) chance that BOTH engines will fail in the same hour.
That is where the redundancy comes into play with dual engines.
You will see twice the engine failures, but you will be stranded 1000 times less because of a failure. (Statistically!)

This assumes that there is Nothing shared between the power systems, especially the fuel tanks.
And don't let a mechanic install the same bad part on both engines.