Twin VS single

[powerabout]

Originally Posted by Stumble

Claydog,

It depends on how you define performance, but there are some advantages each way.

A twin set up

2) More options in installing location allowing for better balance
3) Less weight and thrust at a specific point
6) Less prop ventelation (Not on centerline)

.

Stumble are you talking a twin shaft drive boat as some don't apply to a sterndrive/outboard vee bottom

[Stumble]

Powerabout,

I was refering to outboards not inboards, where the decision is usually made in the hull design phase.

For further explanation;

2) A single engine is almost always installed centerline, though it is possible to bring it closer or further from the hull. For twins there is some wiggle room in exactly where the engines are placed. For instance one boat I know of has a 4 ton crane placed on the starbord side, to correct the list of this heavy piece of equipment the engines were placed slightly to one side to help offset this list.

3) Because the weight of a single engine is concentrated in one area the transom must be strong enough to support the increased load at this point even assuming the net weight to the boat is less than for a twin. On my Catamaran each transom section is built to handle up to 150hp, but neither could handle the weight of a 300hp engine alone.

6) Assuming a traditional V hull (or modifications of it) the hull is at its' deepest point in the centerline. This causes the engine to be more likely to be caught in the hollow created behine the hull than if the engine is placed off center where the hollow is shallower.

[Squidly-Diddly]

what do you mean by 'ventelation'?

Ventilation, as in air getting to the prop? and wouldn't a single at the bottom of a vee have less air getting to the prop than a twin(especially on turns)?

[Boston]

I'm going to jump out of the box on this one and refer back to the original post

I've searched the forum and come with a lot of conflicting information, and not having anywhere near the math skills and overall boat knowledge needed to figure it out for myself, I’m hoping for some help in understanding the pros and cons of a twin engine set up beyond cost and having a backup in case of failure. My question is, is there any performance gain on a twin engine set up over a single, assuming all other variables are the same on a planning hull boa

t?

One possible configuration that has not been considered on this thread yet is a single prop twin engine set up. Sure fuel efficiency is going to be slightly lower in any twin engine set up as friction losses diminish the larger the engine, but having a back up engine is something worth the cost given the possible consequences. Doesn't have to be matching engines or even duel continuous use. The whole question depends on how fast your interested in going. My take would be that bombing around the bay is one thing and open water cruising another, racing is its own animal.

[powerabout]

you could certainly have a twin engined boat at a certain speed uses less fuel than the same boat with a single engine
All to do with the bsfc curves

[Squidly-Diddly]

the two engines, one prop setup was 'slagged' here

[Boston]

Not slagged just not preferred by a couple of people. Diesel engines run best at x percentage of maximum output so having a cruise engine running at max efficiency and another for times of need ( high waves, wind, squalls, in a hurry and so on ) seems perfectly reasonable if you also can marry them together on a single prop with a light weight and simple V belt system with clutch. which was also proposed on another thread. That and 360° capable swiveling saildrive which eliminates the need for a transmission. Reduction can be handled with the pulley ratio's. Depends on the size of the boat but V belts seem like a cheep and easy solution.

[powerabout]

Originally Posted by Squidly-Diddly

the two engines, one prop setup was 'slagged' here

Theres are quiet a few PSV and anchor handlers out there with 4 engines and 2 props to overcome the large engine doing nothing is a waste of fuel problem.

[whitepointer23]

i had a tour of an antarctic trawler once and that had 2x 2000 hp deutz diesels coupled to one prop shaft, i think they had there own clutch each to disconnect . i can see this would be a good idea on these ships that do 12 week trips, just shut one down for service and repairs while steaming on the other one.

[Submarine Tom]

It really depends on the application now doesn't it.

-Tom

[yipster]

On a single counter rotating dual props avd some extra grip and power, they also take the propwalk out
A small emergengy ob is often carried as homecomer, not so great when wheather changes quikly and your way out

[yipster]

from boattest i read about the ZF marine single pod http://www.boattest.com/engine-revie...2800-Pod-Drive