if you put a sailmast with sails on a powerboat what would happen?

[minaret]

Originally Posted by Uncle Bob

As a Fisher owner I am obviously biased but I have had several keen sailers onboard who have commented on the unexpected sailing performance. For example "This thing sails better than I expected" and " 5.2 knots out of 9 knots wind speed, can't complain about that"

I too am obviously biased, but there is no reason a motorsailor cannot be designed to sail just as well as a pure sailboat. My Nauticat 52 is a Sparkman and Stephens design drawn by Olin himself (it took him 3 1/2 years to finish, his longest production design period), the hull molds came from Nautor (builders of Swans), it was the hull for the Nautor 53. She sails like a champ, I have one of the tallest rigs in our huge marina. Sails at 8 knots in fairly light air all the time, points quite well, etc. etc. She just also happens to have a very large engine and 450 gallons of diesel onboard, as well as a spacious pilothouse that you can actually see over the bow from. No reason you can't have great performance under both sail and power, they are not mutually exclusive.

[David_Old_Jersey]

Most modern sailing boats are motosailors.......by design! (they are just not marketed with that tag as has a rather outdated / negative image).

A Motorsailor is simply a sailing boat that can make passages at pretty much hullspeed under power.....in the "olden days" (50's and 60's ) to do that needed an inboard engine the size of a small elephant , which dictated the size and shape of the hull which impacted negatively on sailing performance.........but once inboard diesels got smaller and more powerful they could be fitted into sailing boats without the same hull compromises, hence the decline of the Auxilliary Sailing Vessel (a Sailing boat with a small / low powered engine that was not intended to be used as a passage maker - but motor fitted into the available space, and very useful for approach a port / docking).

The stuff on the top of the boat (Wheelhouse / rig size) really being a secondary thing - mostly wrapped around the fact that if someone wanted a boat that could travel on passage at hull speed under motor (instead of sailing) the boat could carry a few more mod cons onboard and would palso robably attract those who wouldn't want to sit in the rain on passage - an approach that might be fun under sail, but kinda loses something when under motor.

In regard to OP the answer is.....depends Certainly would not be an adequate passage maker, even in good weather. and probably lethal in bad......but for floating around the bay under sail would have some merit.

FWIW, me father's old boat was a 27' ex-ships lifeboat rigged as a "Motorsailor" (40?hp of Perkins 4107) and sails. and she drew 2' 6".....sailed well enough in a f5 (downhill ), anything less and progress was more sedate ....in both cases a lot of the progress was sideways! (Keel does a bit more than simply stopping the boat falling over).

[Ike]

The thing to keep in mind here is that the motorsailers mentioned (alden, Stephens, etc) were designed by professional naval architects. As was said

The info you need to get a better idea of stability is all on the web.
Things like center orf gravity, center of effort, center of lateral risistance, righting moments, lever forces, are all there.
I think it would be an interesting project.

Unless you have an engineering or math background I would suggest you hire a naval architect to do this. Putting a mast up is only a small portion of what needs to be done. If you want it to be useful at all, someone needs to do the stability calcs, and also they need to look at where and how this is going to be placed, where the centers of resistance of the hull and center of force on the sails are in relation to each other, and how the mast will be supported. The last thing you want is that mast suddenly coming down. If you step it on the cabin top, will there need to be some supporting structure inside to keep the cabin top from collapsing? if it is stepped on the keel, what about the mast step, and the hole in the cabin top? How will you keep the water out? What about stays and shrouds? Where will they be anchored. Will you need chainplates? There are a lot of questions that need to be answered. It isn't just putting a stick up with a rag on it. Sure it can and has been done. Sometimes with great success. Someone mentioned MacGregor. I don't like them much either (neither fish nor fowl) but I must admit he has sold a lot of them, and the people who own them seem to love them.

If you want some professional designers and builders opinions post this question on BoatDesign.net Boat Design Net - the Boat Design and Boat Building Site

[Blue Stocking]

Nothing stopping him from getting an idea, in the first instance, of the meaning of all those terms the architect is going to bill him for.

[Dockhead]

Originally Posted by sdowney717

What interested me was seeing this picture.
That boat looks very similar to my 37 egg harbor sedan cruiser from 1970 which is a wooden boat I rebuilt completely, framing etc...


I have an almost full length keel which is about 2.5 feet in height at the stern end and runs from stem to about where the prop struts are bolted on the hull.

I could imagine a mast up where the front cabin starts about 6 feet back from the stem. Or stepped right in front of the sedan windows as in the photo. It would need to be stepped on the cabin roof or it would block too much interior access. So I dont know if that is doable.
Anyway If it would not simply roll over thrn who knows what I might do someday with this. I was talking with another boat owner who suggested the boat would tip right over on its side since a sail boat has a heavy keel, so was curious what others thought.

You could bolt a lead keel plate to the bottom of the keel.
But why bother if you dont have to do that?
Right now boat draws 3.5 feet and weight 17,000 pounds. Carved into the wood structure someone wrote "15 tons net" but I know the boat does not weigh 30,000 lbs.

Any more thoughts besides it being a dum idea?

It probably is a dumb idea from an economic point of view - should be cheaper, better, and a he'll of a lot less trouble to sell that and buy a purpose built motorsailer.

From technical point of view, maybe not so dumb. You will need help from a pro designer, because the center of effort, center of gravity, stability, will really need to be properly calculated if you want it to be safe and sail at all.

I don't think you would need to ballast the keel; that keel looks ok to me for this purpose, understanding that you will never sail to weather, and the mast must be much lower and the sail area much less than a pure sailboat of comparable length.

[Dockhead]

Originally Posted by David_Old_Jersey

Most modern sailing boats are motosailors.......by design! (they are just not marketed with that tag as has a rather outdated / negative image).

A Motorsailor is simply a sailing boat that can make passages at pretty much hullspeed under power.....in the "olden days" (50's and 60's ) to do that needed an inboard engine the size of a small elephant , which dictated the size and shape of the hull which impacted negatively on sailing performance.........but once inboard diesels got smaller and more powerful they could be fitted into sailing boats without the same hull compromises, hence the decline of the Auxilliary Sailing Vessel (a Sailing boat with a small / low powered engine that was not intended to be used as a passage maker - but motor fitted into the available space, and very useful for approach a port / docking).

The stuff on the top of the boat (Wheelhouse / rig size) really being a secondary thing - mostly wrapped around the fact that if someone wanted a boat that could travel on passage at hull speed under motor (instead of sailing) the boat could carry a few more mod cons onboard and would palso robably attract those who wouldn't want to sit in the rain on passage - an approach that might be fun under sail, but kinda loses something when under motor.

In regard to OP the answer is.....depends Certainly would not be an adequate passage maker, even in good weather. and probably lethal in bad......but for floating around the bay under sail would have some merit.

FWIW, me father's old boat was a 27' ex-ships lifeboat rigged as a "Motorsailor" (40?hp of Perkins 4107) and sails. and she drew 2' 6".....sailed well enough in a f5 (downhill ), anything less and progress was more sedate ....in both cases a lot of the progress was sideways! (Keel does a bit more than simply stopping the boat falling over).

With the abaft the beam and a decent F6 blowing, I think he could make perfectly good passages in that.

I agree with you, that our boats really are motorsailers. I think most modern sailboats of the last 20 years motor very well. And some of them sail very well too - so there is less compromise involved. My boat sails very well (light years better than my previous one) and I now make passages even dead upwind under sail, something I could never consider before. But she motors very well as well, not at hull speed (which is very inefficient) but at 7 1/2 to 8 knots, with the smooth 100 hp Yanmar almost inaudible in its soundproofed engine room. I motored 100-odd miles once from Salcombe to Perros-Guierac in a dead calm - it was a pure pleasure.

So getting back to the OP's question - even a regular sailboat might serve your purposes, better than a cobbled-up modification to a motorboat.

[Jim Cate]

Another issue not yet addressed is the rudder. Your pix don't show it, but many motor boat designs have rather small rudder blades placed in the propwash. The accelerated flow from the prop makes the small blade more effective. Most sailboat designs have much larger area rudders to provide enough lift to turn or stabilize the boat on course.

Something else for the putative NA to address.

Cheers,

Jim

[Stumble]

At least downwind hull shape isn't critical so long as the ship has significant ballast. The question as to how it will sail, at least off the wind will be determined by sail area/displacement ratio. The more sail area the more power it can generate...

Upwind most powerboats have very high initial stability and very low additive stability,while sailboats have low initial stability and high additive. This is a function of hull shape, and keel weight, so any significant changes to them require radical redesign of the hull. Doable but expensive and likely not worth the investment. Of course here the more sail area the more righting moment the boat needs to off set it, and the poorer a power boat will perform.

There are some other considerations, that need to be addressed as well.

1) Power boats do not need the reinforced stringers that a sailboat does to handle the loads of stays. You might find a particular boat has reinforcements strong enough, but it would need to be confirmed. Obviously the larger the rig the bigger a problem this is.

2) you have to figure out where to mount the mast step. The keel on most powerboats is not reinforced to handle the point loads of a mast. They can be rebuilt of course, but this would need to be checked. The bigger the rig, and the higher the compression loads the bigger a problem it would be.


As for sailing performance, it would really just depend on the hull shape, and displacement location. The more the boat looks like a sailboat, the better it will sail. But only a NA could really give you clear guidance on what to expect.

Personally I think much beyond a steadying sail (which are great) would likely be cost more thatch it would be worth to me. If I really wanted this combination I would just look for a motor sailor, or a sailboat with a relatively powerful engine. So long as you are happy with displacement speeds it doesn't take much to get a decent hull shape up to hull speed.

[Fountain 47SC]

What about adding leeboards or daggerboard?

[kavw]

Originally Posted by sdowney717

What interested me was seeing this picture.
That boat looks very similar to my 37 egg harbor sedan cruiser from 1970 which is a wooden boat I rebuilt completely, framing etc...


I have an almost full length keel which is about 2.5 feet in height at the stern end and runs from stem to about where the prop struts are bolted on the hull.

I could imagine a mast up where the front cabin starts about 6 feet back from the stem. Or stepped right in front of the sedan windows as in the photo. It would need to be stepped on the cabin roof or it would block too much interior access. So I dont know if that is doable.
Anyway If it would not simply roll over thrn who knows what I might do someday with this. I was talking with another boat owner who suggested the boat would tip right over on its side since a sail boat has a heavy keel, so was curious what others thought.

You could bolt a lead keel plate to the bottom of the keel.
But why bother if you dont have to do that?
Right now boat draws 3.5 feet and weight 17,000 pounds. Carved into the wood structure someone wrote "15 tons net" but I know the boat does not weigh 30,000 lbs.

Any more thoughts besides it being a dum idea?

15T Net, is the volume of the boat 100ft^3 being a net ton, no one cares about the oats mass, but rather its volume/cargo carrying capacity for taxes and regulations.