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Old 25-07-2011, 23:40   #1
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Why Not Build a Motor Boat Like a Sailboat ?

Well why not?
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Old 25-07-2011, 23:43   #2
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Re: Why not build a motor boat like a sail boat?

They're called trawlers ....
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Old 25-07-2011, 23:47   #3
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Re: Why not build a motor boat like a sail boat?

Except they don't need the lead in the keel.
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Old 26-07-2011, 00:11   #4
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Re: Why Not Build a Motor Boat Like a Sailboat ?

Wouldn't the mast and rigging be rather superfluous?
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Old 26-07-2011, 01:06   #5
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Re: Why Not Build a Motor Boat Like a Sailboat ?

You mean like the Dashews have done?

DashewOffshore.com - the serious cruising sailor's website
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Old 26-07-2011, 01:27   #6
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Re: Why Not Build a Motor Boat Like a Sailboat ?

Motor boats are usually planing hulls (except for trawlers). Displacement hulls are limited in speed by the length of the waterline. Therefore, a motor boat with a sailboat-type hull would be very slow for a power boat. Also, the shape of the hull would allow it to heel very easily. That's fine on a sailboat but I don't see any advantages of designing a motor boat with these characteristics. Motor boats have a different purpose than sailboats. They are generally used for water-skiing, fishing, scuba-diving, and general pleasure boating involving the ability to go fast. I don't think a sailboat hull ideally suited to any of these purposes. Perhaps someone with more knowledge of power boats and hull designs will be able to explain better than I.

by the way Cal40John, the link to Dashew's was very interesting. Amazing engineering.
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Old 26-07-2011, 01:58   #7
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Re: Why Not Build a Motor Boat Like a Sailboat ?

Try looking at Scottish, Danish and Norwegian trawlers, the motor powered boats are very similar to sailing boats. Many of the sailing boats were converted to motors and are still working today.
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Old 26-07-2011, 02:20   #8
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Re: Why Not Build a Motor Boat Like a Sailboat ?

Actually they are called motor sailors and can be as boxy or as sleek as you wish.

They can make a great liveaboards and an efficient passage maker...especially to weather.
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Old 26-07-2011, 09:24   #9
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Re: Why Not Build a Motor Boat Like a Sailboat ?

@Cal40jon, that is exactly what I'm talking about. @Pelagic that is a beautiful boat.

The reason I asked is there were a couple of threads about trawlers, and people were saying that a sailboat is going to be more blue water worthy than a trawler. Looking at trawlers they don't look like sailboats. Don't get me wrong I love the look of some like the Nordhavns and expedition yachts. But I was wondering why not make a motor boat with the same shape. I don't know any modern sailboats that don't have motors. So why not take down rigging, add more fuel in place of it's weight. This is just pure curiosity though.
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Old 26-07-2011, 09:34   #10
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Re: Why Not Build a Motor Boat Like a Sailboat ?

Quote:
Originally Posted by Lexam View Post
@Cal40jon, that is exactly what I'm talking about. @Pelagic that is a beautiful boat.

The reason I asked is there were a couple of threads about trawlers, and people were saying that a sailboat is going to be more blue water worthy than a trawler. Looking at trawlers they don't look like sailboats. Don't get me wrong I love the look of some like the Nordhavns and expedition yachts. But I was wondering why not make a motor boat with the same shape. I don't know any modern sailboats that don't have motors. So why not take down rigging, add more fuel in place of it's weight. This is just pure curiosity though.
You don't want to just take the mast off. As the sailors found out in the 79 Fastnet disaster, no mast is a bad thing. Once they lost their masts they thought, good the motion will be easier, it got much worse. As much as 50% of the moment arm was in the mast. Moment arm is what slows the rolling action. Read the Dashews page as they discuss the mods to make the hull design work as a motor boat.

I thought it was scary when I read that trawlers would add weight up high to increase their roll moment to make the ride easier in the ocean, the only minor problem that they apparently didn't care about was how much easier it was making it to capsize the boat.

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Old 26-07-2011, 09:47   #11
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Re: Why Not Build a Motor Boat Like a Sailboat ?

In my ill spent youth I had a 16' Bahama dinghy that the mast had been removed from and a little 10hp Palmer inboard installed. I had a lot of fun with that little boat and learned a lot about handling a single engine boat. One time after a hurricane had passed I ran it outside just to see how it handled big water. It did a lot better than I did. That was a dumb thing to do!
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Old 26-07-2011, 10:40   #12
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Re: Why Not Build a Motor Boat Like a Sailboat ?

When I'm on a power boat, I prefer to spend time on the flybridge.
Too noisy down inside.
On a sailboat, we don't mind being down low because we get to turn the engine off most of the time.
Can't do that on a power boat.
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Old 26-07-2011, 14:36   #13
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Re: Why Not Build a Motor Boat Like a Sailboat ?

Have a look at the "Gulfstar" trawlers.
They are built on a sailboat hull and have ballast.
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Old 26-07-2011, 14:38   #14
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Re: Why Not Build a Motor Boat Like a Sailboat ?

The most wanted thing in any boat is internal volume. On a sailing boat, you can't go very far this way because it would severely compromise performance. But it is possible to design a power boat with a fairly boxy hull: you just have to add more engine power to reach the same speed.

Then, if you design a power boat with a sailing boat hull, you will lose a lot of volume for little gain elsewhere.

Regarding stability and motion in a seaway, this is something to consider carefully, even on very large ships. In the last century, USS Midway (CV 41) had been fitted with bulges at the waterline, that so much increased her stability that her rolling motion became brutal, to a point that aircraft were thrown overboard. Finally, the ship was scrapped. A naval architect has to carefully manage the hydrostatic stability of a ship, as well as the inertia (distribution of mass), to reach a predetermined roll period.

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Old 26-07-2011, 15:12   #15
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Re: Why Not Build a Motor Boat Like a Sailboat ?

Quote:
Originally Posted by Lexam View Post
Well why not?
Because you don't have to be restricted by the hull shape required for a sailing boat (to sail )........and therefore the boat can have a bigger volume for the length (vs a Yacht). Size sells.
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