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Old 08-30-2015, 11:09 AM   #1
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"Trawleurised" a semi displacement or a planning hull !?

"Trawleurised " a semi displacement or even planing hull!?
Possible ou utopic ?
If I take a look at the selling price of a second hand"planning" motor boat and the price of the motor boat with the "stick" "trawler" or "greensomething" , for the same size, same age a "planning" motor boat is actually discounted at the fraction of the selling price of a "trawler " one.
But if we take a closer look, exept for the boats like the Passagemakers Litle 56, Longcours 62 , Dashew 64', Garcia 54 etc who keep a reasonnable consumption, under the Flag "Trawler" we can find some boat (at similar size) who have horse power, more windage, heavier, mostly beamer and a fairly big consumption per mille !
Hence my question, rethinking the transom waterline, propellers, engine setting, would not it be possible to optimize a "planning hull" to make her at least almost similar (in lt per mille) than the trawler having similar charactéristics ?
At the "hull speed"
Or "worst " by how much 10%, 15%, 20% !?
 
 
For example some boat classified under the name "Yrawler" we can find :
- Séléne 53 43T 405 cv 3,2 lt/mille à 10 nds
- Etoile 65'(cata) 30T 2X250 cv 4,3 lt/mille à 10 nds
- Less 83 55T 325cv 3,7 lt/mille à 10 nds
- Swift Trawler42 2X300 cv 3,3 lt/mille à 10 nds
- GB 41 EU 2X425 cv 5,1lt/mille à 10 nds
- Greenline 70 2X800 cv 5,6 lt/mille à 10 nds
- Sunreef 70 2X800 cv 4lt/mille à 11 nds
- Adagio 58 2x575 cv 4,7lt/mille à 10,4 nds
- Swift Trawler 50 2X435 cv 4,1 lt /mille à 9,1 nds 7,4lt/mille à 16,5 nds
- Grand Bank 2x715 cv 6lt/mille à 10nds
(oups forgot the model !)
- Rhéa Trawler 47 2x350 cv 4,7lt/mille à 9,8nds
- Séléne 62 2X715 cv 2,9lt/mille à 10,5 nds !!??
- Sélène 66 610 cv 4,6lt/mille à 10,4nds
- Sélène 54 2X405cv 7,6li/mille à 10,4nds
- Ocean Alexander 60Classico
2x550 cv 9,3lt/mille à 11?7nds et 6,8lt/mille à8nds
- GB 52 EU 2x567cv 6,4lt/mille à 11,2nds et 3,25lt/mille à 9,2nds
- GB Aleutian 53 RP 2x836cv 7,45lt/mille à 11nds
- Swift trawler 52 2x575 cv 4,6lt/mille à 10,4 nds
In another hand one optmised hull ( ok it is just one extrem for the fun )
Stromfugel Fulmar à 58nds 4,1lt/mille
More "classics" planing hulls :
- Fairline Squadron 48 2x435cv 2,4lt/mille à 9,2nds
- Princess V48 4,9 2x435 cv 4,9lt/mille à 10,5nds
- Sarnico 60' 2x1000cv 5,33lt/mille à.....15nds !
 
After reading these resume it is clear that some still receive the name " trawler " but they consume more and have bigger engines than many "fast" motorboats and sometimes even with much smaller tanks !
And for the difference of the hull line some are very close just the deck plan and superstructure change

Sorry for my English today it is worst than normally !! How said it is not possible !!
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Old 08-31-2015, 08:41 AM   #2
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Optimize, schmoptimise!


We just go slow when we want to.


OK, so the hull form isn't perfectly comfortable in all sea states at slow speeds. Tough; we get over it. Or else tack. Or else speed up. Whatever.


No agony required.


-Chris
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Old 08-31-2015, 09:23 AM   #3
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Thanks for answer

Quote:
Originally Posted by ranger42c View Post
Optimize, schmoptimise!


We just go slow when we want to.


OK, so the hull form isn't perfectly comfortable in all sea states at slow speeds. Tough; we get over it. Or else tack. Or else speed up. Whatever.


No agony required.


-Chris
Did you check your consumption at "low speed" worst than trawler boat ? If yes by how much ?
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Old 08-31-2015, 10:16 AM   #4
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Fuel consumption for full displacement "trawlers" is fairly consistent. Using the data in Bebe's book, Voyaging under Power, you get about 1,5 hp per 1,000 lbs to reach hull speed.


Semi- displacement hull trawlers (those with a flat deadrise aft and little rocker) use more fuel- about 2 hp per 1,000 lbs. There is no free lunch and if you want to go fast you have to pay the price of a less efficient hull while going slow.


I don't know about planning hulls, probably even worse, but who drives a planning hull at hull speed.


David
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Old 08-31-2015, 12:45 PM   #5
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Quote:
Originally Posted by longcours62 View Post
Did you check your consumption at "low speed" worst than trawler boat ? If yes by how much ?

I don't have fuel flow scans, but I've checked using nominal performance curves for our engines.

Our WLL is 43.875' so theoretical "calculated hull speed" is approx. 8.87 kts.

At 1200 RPMs (approx. 8.9 kts) we get a nominal fuel usage of 1.53 NMPG.

At 900 RPMs -- approx. 7 kts, and closer to (1x sqrtWLL) -- we see a nominal fuel usage of 2.35 NMPG.

More often, we run at about 1000 RPMs, approx. 7.5 kts, 2 NMPG.

Depends on sea states, though.

"Trawlers" can do better, but I don't much care... because the differences between FD and SD (or SP) versus what we see... don't create much of a blip on my radar.



Quote:
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I don't know about planning hulls, probably even worse, but who drives a planning hull at hull speed.

See avatar and see above.



-Chris
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Old 08-31-2015, 02:05 PM   #6
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Quote:
Originally Posted by djmarchand View Post

I don't know about planning hulls, probably even worse, but who drives a planning hull at hull speed.


David
Damn near everyone that has a boat over 35 feet. I run mine on plane though.
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Old 09-01-2015, 06:51 AM   #7
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Did you check your consumption at "low speed" worst than trawler boat ? If yes by how much ?

The poor shape of a plaining boat is mostly extra surface area , penalyu perhaps 15%

The vastly over sized engine running at just above idle , another 15%.

So a 6k cruise that might cost a displacement hull 3 gph may cost the go fast 4 gph.

Not bad , till you figure in the cost of reducing the engine service life 50% or more.

A 5000 hour engine might be slobbering at 2500 hours , but at the usual 200 hrs per year , its a decade away.
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