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Old 03-03-2014, 15:21   #16
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Boat: Devlin 48 Moon River,j/100 BJ
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Re: Semi Displacement vs Planing

My present boat has a hull which is considered a fast semi displacement type (very similar to a DE lobster boat). What that means is the hull is happy at and below its hull speed of 9 knots and acts comfortably as a displacement hull. When more power is applied part of the hull lifts out of the water(not as much as a full on planning boat) and on my boat speeds up to 22 knots are obtained (with bigger motors 30K would not be unusual for this hull type). The fuel burn at the 16-20 K range appear to be similar to planning boats of the same size and weight. The big difference is that I cannot exceed 22K and in the range of 9-16K my fuel burn is significantly better than a full on planning boat. A planning boat that is not over the hump gets poor fuel burn with a big wake and improves once over the hump. As I see it if you like or need to travel at high planning speed you need a planning hull but if you spend any significant time at 7-16 K you would do better with a semi and probably have a more seaworthy vessel.
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Old 03-03-2014, 15:31   #17
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Re: Semi Displacement vs Planing

I doubt that if one can afford a 200k pound boat 75 pounds an hour for fuel at economy planing speed would be an issue. One could probably afford to go for a jaunt for a few hours.
The limit in the canals is 8 km/hr or 5 mph. For a motor of four fifty hp that is barely an idle - hardly good for longevity.
Still nice boat.

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Old 03-03-2014, 16:10   #18
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Re: Semi Displacement vs Planing

Sorry to disappoint you but it's not a new boat!
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Old 04-03-2014, 02:48   #19
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Semi Displacement vs Planing

The aquador 32C is a lovely boat, and will do what you want . I'd recommend it. More then adequate to nip across the channel and handy enough at low speeds. You'll need the power to to handle the rivers in France especially the Seine and the Rhone, a displacement boat is very limiting and I wouldn't reccomend it. The faster boat will be generally more useful too in those time limited weekend trips along the coast etc.

Not to mention the fact that displacement mobos have little value in the UK, nobody on the coast buys them.

Most aquadors are big single engine versions a few were twins. Carry a transom mounted outboard for backup on the channel crossing.

The big engine will be fine pottering about. Once she isn't new and has been broken in properly, the turbo after a while ( years) might get coked up , but nothing that can't be fixed. I presume you will be doing paris , so just check the overall height, she's near the limit , the little arch may have to come down. Lovely boat for a couple.

Transom stern boarding is handy and you have aquadors lovely quality.

I'd say your making a wise choice. What is she engined with D6 Volvo or yanmar?

Several posters have commented that semi displacement Has better sea keeping . These days that is not true anymore and the arrival of large deep vee planing hulls has disproved that theory.

Look at the newest all weather pilot boats and the new Shannon class RNLI lifeboat. All are deep v planing hulls. Not to mention the big tough as boots RIBs. Planing hulls are considerably at fuel economy at planing speeds then semi displacements running fast ( ie > 12 kn)

One of the experts on heavy weather mobo usage , dag pike ( his book is a good read) prefers planing hulls in bad weather over semi displacement.

Having been out on the new RNLI boat, one can only agree with him


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Old 06-03-2014, 12:01   #20
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Re: Semi Displacement vs Planing

I am thinking the deep v hulls and the fast semi displacement hulls are inching toward each other and the differences are probably in degrees of v in various parts of the bottom and the size of the motor. Therefor both will have better sea keeping than the old school planning hull. The more radical V bottom will usually need more power particularly if high speed is desired while the fast semi displacement hull usually is fitted with less power with high cruse speed target in the mid to high teens while deep v aims at mid 20s and way up. A fast semi displacement hull can be powered for higher speeds as the racing lobster boats and the newer breed of DE boats clearly demonstrate all that's needed is the big diesel.
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Old 09-03-2014, 14:18   #21
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Re: Semi Displacement vs Planing


I have owned Sealine And Fairline planning boats as well as traditional wooden displacement boats, so hope this helps a little , the deep v on the Fairline Targa handled a F7 in the channel safely coming back from the Scillys. The 340 hp was a big bonus when staying in the trough of breaking waves if not a bit thirsty she would stay on the plain at 14 knots with full tabs down, not sure a semi displacement would pull out of a broach on a surfer in those conditions, this is pure guessing as I have never driven one, but saying that you can always wait for the weather on a Chanel hop.
My choice would be the Targa (brand name .. Not the Fairline model) they call it the 4x4 of the sea, never helmed one but seen them perform and was impressed

Personally I would always go twin engined if you are going to do any decent passage, I have tried an outboard auxiliary , waste of time , in my opinion, if its powerfull enough to provide more than steerage , it will be to heavy for the transom / bathing platform or to manhandle and stow. It also means carrying petrol in enough quantity as a back up which would not be my choice, they also lift out when in any decent sea .

What ever your choice I am sure you will have a great time, happy cruising

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displacement, men

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