What Are Outdrives For.

[hlb]

Now I can understand outdrives on trailable boats. Also understand there use on smallish boats on drying moorings.
Theres an advantage if a rope gets round the prop. Cos just lift it up and throw off the rope. But I dont see many 30ft plus boats layed on there sides on the beach. So whats the point of hanging all this expencive metal in the water. Sending massive amounts of power round torcherous bends. Engine sat at the back instead of nicely in the middle. A few threads down, folks were talking about them being harder to steer and needing a bow thruster as well. I might be a bit thick here. But I've had both outdrive and conventional drives. The out drives fly in the air on bits of waves where as the propper ones hardly ever come out the water. The weights in the middle so the nose dont jump up when going over waves. So whats the point of having these very expencive. prone to breaking thingies. Stuck on the back.

Have you sent off Your Stamped. SAE and cheque. Yet.

Haydn

 

[oldgit]

How about simple to install in boat.No skilled labour etc.Just cut big hole using template and bolt in.No aligning beds/shafts/P brackets etc.Also takes up less room wedged at back of boat even if it does bugger up C of G etc.and can somebody explain why boat with legs is always faster than one with shafts.

 

[adarcy]

Dear Haydn

One of the reasons is that they are much easier for manufacturers to fit, i.e. cut a hole in the back and "slip in" a pre-prepared package and you don't need separate rudders.
Another is that they are more efficient - less underwater drag when on the plane, no shafts and p-brackets (perhaps refer you to the recent Sonny Levi article in MBY) - also the thrust is in line with the direction of travel e.g. forwards whereas shafts run at 15 or so degrees down, so a componenet of the power is always trying to lift the boat up instead of leaving the hull to do it.

Against that, they can only transmit so much power, or more importantly, torque and they are only a half-way house to the real biz of surface drives (see the Baia tests in MBY again)

About 8-10 years ago MBY did a test on the Fairline Corniche with petrols and diesels and shaft v sterndrives. The sterndrives were the faster but they did mention more "nodding" effect and needing some trimming to counteract the stern weight.

Anthony

 

[hlb]

Oh thats a bit I forgot. Yes it goes a bit faster cos the props are facing backwards and not a bit downwards as with proper props.

Have you sent off Your Stamped. SAE and cheque. Yet.

Haydn

 

[jfm]

Re: drag

1. Easier to install, as oldgit says. Bit like a fwd car, you wd think more complex becos of univ joints etc but actually cheaper to make becos all done as sub assembly then throw it under the bonnet, no bits to connect up hardly
2. Accommodation easier to plan, as oldgit says
3. Quite a lot less drag than a P bracket and shaft etc, and thrust points in right direction, so faster for same hp. People think this is a small point, but it's massive. In a 40 foot twin shaft boat at 30 knots you are probly expending 100-150bhp + just to drag the p brackets, rudders and shafts through the water

The issue about gearbox in water seems overstated. There are zillions of these installed, and generally they stay in one piece.

 

[hlb]

So what your saying is we dont want them, but the boat builders do. Yes I know about the go a bit faster bit just forgot to mention it first time round. and then you beat me to it.
Anyway like I said. Why should we want them. Not why do we get them.

Have you sent off Your Stamped. SAE and cheque. Yet.

Haydn

 

[trev]

I've had both outdrive and shaft driven boats and, honestly, I find it doesn't really matter a toss!!

Trev

 

[Deleted User YDKXO]

Compare this. You can buy a Princess V42 with 370hp inboard engines and do about 35knots or you can buy a V42 with 260hp outdrives and do, er, 35knots plus it costs a lot less. As jfm says the efficiency loss from all that stern gear on a shaftdrive boat is horrendous
The other major reason for fitting outdrives is interior space. Coz the engines are at the back you can get an aft sleeping cabin in a 30' sportsboat plus a much lower coachroof
Having said that give me shaftdrives any day for reasons thrashed to death already

 

[duncan]

more like 7 degrees on shafts I thought?

also trimmed in an outdrive can have more than this and help the relationship between power and getting on the plane...