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Old 02-04-2011, 23:53   #1
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Small Full Displacement Cruisers

hello. looking around i see a lot of semi-displacement or planing hulls in the 20-30ft, but not so many full displacement cruisers.

what production boats or models that are full displacement under 30ft that you guys would recommend or just want to talk about.

anything you want to point out or talk about with dealing with sub 30ft full displacement cruisers are good.

any reason not to have a full displacement boat under 30ft?

John
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Old 03-04-2011, 03:49   #2
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Re: Small Full Displacement Cruisers?

28' Bristol Channel Cutter

THE WORLD'S BEST SAILBOATS: A book by Ferenc Mate. "Sam L. Morse Co.". A personal opinion of the Bristol Channel Cutter. "I might as well start off by telling you that the Bristol Channel Cutter and the Falmouth Cutter are the most beautiful 28 and 22 foot fiberglass boats in the world... If you look at the lines of the Bristol Channel Cutter, you will see she reaches maximum beat well aft of the mid station, and her entry lines are straight, very much like the best of modern cruisers... As to how well she handles, all you have to do to answer that question is read the Pardey's books, for they sailed her without an engine all over the world, which means a lot of mean light tacking in mean tight harbors, and they came back to the same design again".


Review here http://samlmorse.com/?a=boat_us


Fast, seakindly, built as good as can be. And she is a beauty!

Disclaimer: I have one.
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Old 03-04-2011, 07:17   #3
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Re: Small Full Displacement Cruisers?

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28' Bristol Channel Cutter

[FONT=Verdana][SIZE=2]THE WORLD'S BEST SAILBOATS:
...
You probably look at posts from the portal, and didn't notice that this thread is in the "Powered Boats" forum.

@ samson - That's the type of hull I'm interested in, but I am looking more in the 36-40' range. I'll let others reply. I'm sure they will.

-dan
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Old 03-04-2011, 08:22   #4
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I really like the Prairie 29, which is also the Atlantic 30. Solid hull, Hargrave design, excellent storage. Some come with twin engines, galley position can be up or down, some have only flybridge steering, some only an inside steering station, I have seen one with a door by the inside station, one with a transom door, etc. Lots of options.
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Old 03-04-2011, 09:28   #5
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Re: Small Full Displacement Cruisers?

You are correct, there are very few production full displacement cruisers. In additionto the Prairie, the Willard 30 is another one.

The reason that there are so few is that in that size range or any size for that matter, the rounded hull shape of a full displacement hull limits interior volume. The hard chines of a semi displacement hull add considerable useful width and volume.

But what functional characteristics are you looking for? The rounded hull types are efficient at low speeds, but roll a lot in heavy seas. The hard chine boats are less efficient and can have a sharp rolling motion.

The hull type that I like is a downeast style hull- full keel to protect the prop and a soft chine which softens the rolling motion.

One of these that might fit your needs is the Cape Dory 28 with the 100 hp Westerbeke. The engine hp limits it to displacement speed and should be reasonably efficient. I have one, but with a high hp gas engine and the interior packs a lot in a small space.
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Old 03-04-2011, 18:54   #6
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Re: Small Full Displacement Cruisers?

I think another reason you don't see many is that it's pretty hard to live aboard for any length of time on a 20-30 foot boat. I think 30-40 is where it starts to be a lot more practical, and the amenities go up from there as you get bigger. We had a Back Cove 29 for a couple of years and although it was equipped for live-aboard with stove, fridge, microwave, inverter, shower, etc., it was just too small for anything more than an occasional weekend. We all have different tolerance levels for things, but for us we couldn't see spending a week on the boat, and moved up.

That said, there are other boats that make better use of 20-30' for cruising than the Back Cove. American Tug comes to mind, and other similar boats that I've seen at shows. It's really impressive to see what can be packed into that length.
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Old 04-04-2011, 13:23   #7
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Light, full displacement is the way to go

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Originally Posted by djmarchand View Post
... The rounded hull types are efficient at low speeds, but roll a lot in heavy seas. The hard chine boats are less efficient and can have a sharp rolling motion.

The hull type that I like is a downeast style hull- full keel to protect the prop and a soft chine which softens the rolling motion.
(Real downeast boats are round turn of the bilge to a pretty flat bottom, no chine).

While the "roll a lot" trait is "common knowledge" it also seems to be incorrect. The vessels that must be out in any weather, and must allow people to work, tend to me round bottoms unless the boat must also run at high speed.

Watching various boats drift around fishing, for example, and you'll observe that the round bottom boats (like the true down east boats -- not those styled like down east boats) roll much less than anything else you see out there. More importantly, they roll SLOWER than power cats, hard chine boats, or other boats with high static form stability.

Everything rolls, but the more static form stability (the more stable at the dock), the more the boat follows the surface of the sea, so the more the boat rolls. The worst part is that the roll rate imparted by the sea varies dramatically over the period of the wave: slow in the trough, then very fast as the peak passes beneath the boat. This variability (often called 'snap roll') is what makes such boats difficult to work on, and what leads to seasickness and fatigue. Since most accidents are due to the diminished mental capacity due to seasickness and fatigue, round bottom boats are safer.

That is the reason that seaworthy boats (pilot boats, fish boats, ...) have low metacenter heights. The designer must often specifically work to reduce at-the-dock stability in order to ensure the vessel has a slow rolling motion in heavy conditions.

So, a full displacement boat is probably what one really wants the smaller a boat gets.

However, its simply because gas has been so cheap, and free time so limited, that working people buy faster boats.

Oddly enough, displacement hull does not require heavy displacement. Heavy displacement means the wave speed (hull speed) really limits speed. All the previously mentioned designs are very heavy displacement, so they are really locked in to hull speed.

However, light displacement means the wave drag rise is much less, so hull speed is less noticeable. For example, I once had a Santa Cruz 27. I ordered it from the factory without rigging, so at first it was just a 2800 lbs 27 foot powerboat (with a 1500 lbs lead keel). Hull speed on a 25 foot waterline is 6.7 knots. With a 4 HP outboard, it would go just about 8 knots. That's 20 miles per gallon! 8 nmpg / 0.4 gph = 20 mpg. Once I put the mast up and added all the sailing gear, it weighed about 250 lbs more, and had all that additional windage, so it would only go hull speed (6.7 knots) but still it got 6.7/0.4 = 17 nmpg. Another owner bought a 15 hp outboard, and they went 12 knots, which works out to 12/1.5 = 8 nmpg.

So I expect that we will see many more full displacement (but light displacement) powerboats in the near future.
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Old 04-04-2011, 13:31   #8
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Re: Small Full Displacement Cruisers?

I've always liked the Nordic Tug. Fun little 26 and I think they made a 30 also.
Good luck in your search. Use the search engine after my signature for Nordic Tug.
kind regards,
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Old 04-04-2011, 13:55   #9
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Re: Small Full Displacement Cruisers?

I like the Nordic Tug a lot. However, it just looks like a displacement hull, but is actually a very high resistance hard chine hull, therefore its fuel efficiency is very poor.

My 32' Fountain with twin fuel injected big block gas engines, running at any speed from 12 to 55 knots, gets the same fuel efficiency as a single diesel Nordic Tug 32 running at 12 knots (just over 1 nmpg). At displacement speeds, both boats also get pretty much the same: about 2 nmpg at 7 knots.

It takes work to move a boat. Work burns fuel. An inefficient hull (hard chines, long keel, heavy) takes a lot of work to move, so burns a lot of fuel. The Nordic weighs twice as much as the Fountain, so takes a lot more work to move it. But it has a diesel, which produces about twice as much work for a gallon of fuel (20 hp/gal/hr for the diesel, 10 hp/gal/hr for the gas engines). So its not surprising they both burn about the same about of fuel per mile.

But there is no question that Nordic Tugs are high quality, roomy, well laid out, seaworthy, fun boats. But fuel efficient they certainly are not. They only look fuel efficient.
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Old 04-04-2011, 14:31   #10
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Re: Small Full Displacement Cruisers?

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Originally Posted by u4ea32 View Post
But there is no question that Nordic Tugs are high quality, roomy, well laid out, seaworthy, fun boats. But fuel efficient they certainly are not. They only look fuel efficient.
The Nordics have semi-planing hulls and high-horsepower engines making them capable of speeds well above hull speed. For instance, the 26-foot model has a 115 h.p. engine, easily three times as powerful needed to drive the vessel at hull speed.
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Old 04-04-2011, 14:40   #11
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Re: Small Full Displacement Cruisers?

Here is information concerning the Coot, a hard-chimed, 35-foot recreational trawler:

"A typical diesel will develop almost 20 HP for an hour on one gallon of fuel. Id tend to cruise at about 1.2 or so speed/length ratio. 6 1/2 to 7 knots is a good clip, and the engine will easily do it. Notice the difference between 7.6 knots and 9; that translates to 1.2 gallons an hour to over 7 an hour.....



S/L Ratio..... Knots..... HP
1 ...... ..........5.63........ 3.9
1.1............... 6.19....... 6.0
1.2 ...............6.75....... 9.5
1.25............. 7.03...... 12.8
1.3............... 7.32...... 17.3
1.35.............. 7.6........ 23.5
1.6................ 9.0 ...... 149.3

With a 60 h.p. engine, the vessel is capable of a maximum speed of about 8 knots. At speeds of around 7 knots, consumption should be around one gallon an hour.
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Old 04-04-2011, 14:43   #12
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Re: Small Full Displacement Cruisers?

wow SaltyMonkey likes these tugz alot but is confused by so many options!
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Old 04-04-2011, 15:10   #13
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Re: Small Full Displacement Cruisers?

"Snap out of it!"
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Old 04-04-2011, 22:57   #14
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Re: Small Full Displacement Cruisers?

cool thank you all for all the help.

reading these i have learned a lot.

are there different classifications of a "displacement" hull? like hard chine round chine? what else?

what is a "real down east boat"?

and reading this from the nordic 26 info.

"Though her 115 hp (86 kw) Cummins diesel burns less than one gph at six knots or two gph at eight knots,"

how is that? i have been doing all sorts of numbers and things and im seeing yanmars 20 and 30hp barely burn less then 1gph or around .7gph to put a displacement hulled boat under 30 ft to hull speed. that is a HUGE difference from 30hp to 115hp.

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Old 04-04-2011, 23:34   #15
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Re: Small Full Displacement Cruisers?

Hard to give you an answer unless we know the boats you are referring to. Yes they can reach hull speed with a small engine in flat water which means no wind and no current working against them. Add a bit of counter wind and things change quickly.
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