Drag question........

All right, first post and first question. Cut Me a little slack here as I used all My boating knowledge to answer the no spam question on the sign up page.

I have been looking at motor sailer's recently. They all have a prop hanging off the bottom of them. Since the motor is generally used just for maneuvering around the harbor, Wouldn't it present a large amount of drag while under sail? Do they have feathering props? Wouldn't a pump set-up like a jet boat result in a lot sleeker underside? Am I on crack and over thinking this?

I lied, multiple questions................

 

A sizable prop does have a large amount of drag. It is best to have the prop shaft locked while sailing.
A lot of motorsailor owners just accept the drag penalty as they are not racing. Others do opt for feathering or variable pitch props.
I suppose there may be a few water jets on motorsailors somewhere, but I am not aware of them. A conventional shaft and prop are cheaper and very reliable so that is probably the reason for not resorting to more efficient alternatives.

 

The next question ("more efficient alternatives") is more efficient "when". It is a "motor-sailor", you say, which indicates it is motoring probably more than it is sailing, or, at least, a lot. A feathering prop isn't bad. Jets open up a can of worms you're gonna want to put back. Too big for an outboard?

 

You don't say what size vessel you are looking at. Prop drag is in proportion to the prop diameter and a 70 - 40 (70% on the motoring side) will generally want a larger fixed prop turning slowly.
A 40-70 will be more likely to have a smaller prop and then a feathering prop is affordable and will give you better performance under sail for light and medium air often adding a half to one knot to the speed under sail.

It's all compromises and no absolute hard and fast rules.

 

That just brings up more questions.

Needs to have long range extended time at sea capability's, leaning towrds a multi-hull. Living space versus speed.

 

How so? While I have never owned a jet powered craft, I have worked on quite a few pumps being a machinist. Most of the problems I see with them a maintenance (or lack thereof) related along with the throw away PWC manufacturing standards.

Don't know yet. How big is too big for an outboard?