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Old 01-18-2013, 01:56 AM   #1
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How about a thread on fast or semi-displacement trawlers

Such as Benneteau, Sabreline, Mainship, etc.
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Old 01-18-2013, 07:44 AM   #2
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Why? There's already threads on here about SDH's etc

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Old 01-18-2013, 09:32 AM   #3
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Originally Posted by LoneEagle View Post
Such as Benneteau, Sabreline, Mainship, etc.
Welcome Lone Eagle. Look for the search feature in one of the thin red lines above. Put in your search criteria, and look up most anything. There is a world of info in the archives including semi displacement hulls. You can also check the headings listed by boat manufacturers below.

If you want to start a new thread click on the new thread button, put in a heading, and post away.

How about telling us a little about your self and boating status. That is are you interested in buying a boat or have a boat. Things like that can help get you started. Sick around.

Edit: Just looked back and saw you have a Sabreline 36 near Annapolis. I happen to be partial to Sabres and Annapolis. Look for a private e-mail to show up in your mail box.
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Old 01-18-2013, 11:04 AM   #4
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Well let me offer some thoughts to get the conversation started.

Fast, semi displacement trawlers (to use the trawler term loosely) are the norm today. Very few trawlers are round bottom pure displacement hulls. It is easier to note which are not semi displacement than those which are. Nordhavns, Krogens are two that are full displacement trawlers. Beneteaus, Mainships, Grand Banks, Sabres, Nordic Tugs, etc are all semi displacement.

Semi displacement hulls are able to go faster than displacement speed, but unlike planing hulls they really don't have a "hump" to get over. On the three semi displacement trawlers I have owned, it seems like there is a smooth, exponential relationship between power and speed.

Semi displacement hulls are less efficient than round bottom displacement hulls at displacement speeds. The angular lifting planes on a semi displacement hull just don't let water slide over them as easily as smooth round bottom displacement hulls. Where a displacement hull will take 1.5 hp per 1,000 lbs of hull weight to push it to displacement speed, a semi displacement hull takes 2.0-3.0 hp per 1,000 lbs.

Semi displacement hulls have big engines to push them to 10 kts and above. But can you safely run those big engines slow and cruise at or below displacement speeds?

The question is controversial, but I believe that if you run the engine at enough power loading to keep the cooling water and oil at operating temperatures then you will not do any damage. Coincidently that power level is just about the rpm and power setting needed to reach displacement speed.

So I run the 370 hp Yanmar in my Mainship Pilot 34 at 1,600 rpm and it goes about 7 kts, just below displacement speed. BTW the accepted definition of displacement speed is 1.34 * sqrt(water line length).

Weight becomes a big factor in semi-displacement hull efficiency, mostly because you are using a lot more fuel than a displacement hull at all speeds and much more fuel the faster you go.

It is interesting to note the differences in a low cost, mass produced trawler like the Mainship Pilot 34 and a high end one like a MJM 34. The Mainship claims that the Pilot 34 weighs 15,000 lbs and the MJM claims that their 34Z weighs 10,600 lbs. The difference if is is real is mostly due to fiberglass layup techniques. MJM claims that their 34Z uses 30% less fuel than their competitors and I can believe it if their weight is correct.

Semi displacement trawlers come in several hull types: classic flybridge models like the Grand Banks; pilot house, tug style like the Nordic Tug and downeaster style hardtops like the Mainship Pilot 34. And lots of variations in between.

So, that is a lot of info and maybe it will spark some discussion.

David
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Old 01-18-2013, 11:50 AM   #5
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So I run the 370 hp Yanmar in my Mainship Pilot 34 at 1,600 rpm and it goes about 7 kts, just below displacement speed.

David
I've always been interested in the performance of the Mainship 34 Pilot. Would you please list some of the performance specs such as:

High cruise speed
WOT Speed
Fuel flow at Those Speeds, etc

I'm interested in the single engine specs but either or both would be nice.
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Old 01-18-2013, 12:19 PM   #6
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Originally Posted by SeaHorse II View Post
I've always been interested in the performance of the Mainship 34 Pilot. Would you please list some of the performance specs such as:

High cruise speed
WOT Speed
Fuel flow at Those Speeds, etc

I'm interested in the single engine specs but either or both would be nice.
Walt, I have info on my 2004 Pilot 34. David will have info on his.

I could cruise at 16 knots ang get 1.87 statute miles per gal. I figured in statute miles because the ICW is marked in statute miles. So I could really get an accurate reading. I did some long legged cruising with it. These are approx miles, but i could run from Hilton Head about mile 575 ti Swansboro, NC at about mile 230 or so on one fill up. That is at the 26 knots. You can convert statute to nautical miles for that figure. It was a great little cruiser.
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Old 01-18-2013, 12:19 PM   #7
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Walt:

With the Yanmar 6LY-STP 370 hp engine, my Mainship Pilot 34 will top out at 20 kts and high cruise at 2,800 rpm and 15 kts. Both were measured with two way GPS speeds, 1/2 fuel and water, very clean bottom and two persons on board. I don't have measured fuel consumption, but Yanmar's prop curve indicates about 12 gph at 2,800 rpm which I suspect is pretty close.

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Old 01-18-2013, 12:44 PM   #8
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These are approx miles, but i could run from Hilton Head about mile 575 ti Swansboro, NC at about mile 230 or so on one fill up. That is at the 26 knots.
Did you mean 16 knots? Single or twin?
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Old 01-18-2013, 12:48 PM   #9
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[QUOTE=djmarchand;127701]

With the Yanmar 6LY-STP 370 hp engine, my Mainship Pilot 34 will top out at 20 kts and high cruise at 2,800 rpm and 15 kts.
QUOTE]

I think those are the kind of speeds that I could be real satisfied with.

Thanks, David.
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Old 01-18-2013, 12:59 PM   #10
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David I like your post #4. But "round bottomed" is not at all required for a full disp hull. Mark's Coot is a good example. Flat bottomed boats are frequently FD and w the hardest chines of all. The hard chine basically has nothing to do w it. The thing that makes a full disp hull is the angle of the bottom aft that returns the water gracefully to the surface that identifies the FD hull. If your'e transom is completely out of the water (or nearly so) you definitely have a FD hull. Flat bottoms aft need not apply. A DF hull may ease the water aside at the bow or basically smash it aside (as in punchers or slicers) but if the stern tries to keep the water down it's not a FD hull. A FD hull provides the means for the water to smoothly FLOW along aft and up at the stern. A semi-disp hull's wake at the stern is anything but graceful and flowing. It's a violent frothing mass of water jumping up and down consuming lots of energy.

Here's Willy at top speed and only a trace of turbulence is present in her wake.

95% of the boats here are semi-disp types.
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Old 01-18-2013, 02:12 PM   #11
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David I like your post #4. But "round bottomed" is not at all required for a full disp hull. Mark's Coot is a good example. Flat bottomed boats are frequently FD and w the hardest chines of all. The hard chine basically has nothing to do w it. The thing that makes a full disp hull is the angle of the bottom aft that returns the water gracefully to the surface that identifies the FD hull. If your'e transom is completely out of the water (or nearly so) you definitely have a FD hull. Flat bottoms aft need not apply. A DF hull may ease the water aside at the bow or basically smash it aside (as in punchers or slicers) but if the stern tries to keep the water down it's not a FD hull. A FD hull provides the means for the water to smoothly FLOW along aft and up at the stern. A semi-disp hull's wake at the stern is anything but graceful and flowing. It's a violent frothing mass of water jumping up and down consuming lots of energy.

Here's Willy at top speed and only a trace of turbulence is present in her wake.

95% of the boats here are semi-disp types.
Here is mine at just 9 knots Eric, semi displacement.
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Old 01-18-2013, 03:03 PM   #12
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Did you mean 16 knots? Single or twin?
Right 16 knots. 370 Yanmar . No dinghy or heavy stuff and only 2 people on board. That boat covered enough ground to satisfy us. It was noisier than the Sabre, but we had done no extra sound attenuation. Sweet little boat.
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Old 01-18-2013, 06:24 PM   #13
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Fast or semi-displacement trawlers, sounds like an oxymoron....
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Old 01-18-2013, 07:14 PM   #14
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Bomba,
Nice gentle wake for 9 knots. No doubt a very efficient hull. Looks a bit like Steppen's boat ... Kind of a lobster type. From what I hear and read they are best at about 12 to 18 knots. Nice soft chines, flat and light aft. Lots of the fishing boats have lots of power ..... don't understand it. I would think a 35 to 45' boat w 5 or 600hp would want a more typical hard chine boat. It seems GB thought so re their East Bay series.
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Old 01-18-2013, 07:29 PM   #15
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Question: what differences are apparent in how the different hulls behave in sea conditions and at anchor?
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Old 01-18-2013, 08:32 PM   #16
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I would think a 35 to 45' boat w 5 or 600hp would want a more typical hard chine boat. It seems GB thought so re their East Bay series.
Eric--- You're correct from what I can see of the Eastbays in our marina. They are a fairly typical twin-engine, deep-V planing hull. FWIW here are the lines of the 39' Eastbay (lifted from the GB website). The Eastbay hull was designed by Ray Hunt. The boat can cruise at 30 knots.
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Old 01-18-2013, 08:43 PM   #17
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Walt,

Forgot to mention an important thing. We stored our Pilot 34 out of the water. It always had a clean bottom and running grear. That will make at least one knot difference. Also, the mileage quoted is an average for the overall trip which is a real life scenario.


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Old 01-18-2013, 09:26 PM   #18
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Mainship got the lines right on that Pilot 34 IMO.

What was your opinion of the interior layout Don or David?
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Old 10-14-2014, 09:21 PM   #19
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Here is our Swift 44 running about 16 knots.
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Old 10-14-2014, 09:44 PM   #20
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Such as Benneteau, Sabreline, Mainship, etc.
And we can have another thread about unicorns and gnomes too!
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