Lobsterboat characteristics.

What is it that you find interesting? Any hull is economical to run below its hull speed... It's very un interesting really... What is actually interesting, is that the fuel economy goes down the toilet above 8kts, to an outright maximum speed of 12kts using the full 780hp.... Not sure what the fuel burn is for that, but it ain't good...

Here's one for you, 62ft motor yacht, 18kts max from 300hp... And 4nm per gallon @ 10kts. Surprise surprise, it has a great displacement to length ratio...

http://www.nigelirens.com/boats/power-boats/molly-ban

 

Rusty, these are working craft, often designed to bust butt, more then anything else. They're intended to carry a hefty load, in varying conditions, efficiency is a concern, but more just a cost of doing business, than a major design consideration. They need to be stable working platforms, hence the typical and dramatic warped bottom hull forms and overly large skegs. They can be a handful in a following sea, but anything with a broad transom, carrying a serious load will tend to wallow a bit. Some convert older ones into power yachts and in this, they provide a good bit of internal volume, though still have their "quirks", considering their heritage.

The real question should be what are your needs. These craft have evolved for a specific set of uses, but your needs are what any design choice should address.

 

Sure looks a bit like a lobster boat:

 

Picked it just for you

 

I'm getting close to the big six zero, and I want to build my retirement boat that will see me through till i croak.

I'm not interested in passage making, but would like to do lots of coastal cruising around the med.

12mtrs or less for cheap marina charges.
Soft ride for steep short seas around gibralter.
Single engine.
Lots and lots of volume.
Low fuel consumption at 7-8 kts cruise, but run for shelter at 15 kts.
Hard chine for less roll.
Good in following sea.

New Hull moulding must be available from manufacturer for home completion.

Any suggestions?

 

Start making low offers on stuff like this... Eventually you'll find the right one ...

http://www.yachtworld.com/boats/2009/Armor-RANGE-BOAT-39-HYBRIDE-2684583/CAEN/France#.VB1tCX8aySM

 

Wow that's light at only 4 tons.

Have you got a link to its performance?

 

If you are willing to go to 12 meters, you can get an excellent, comfortable, high capacity displacement hull that will go 7 knots very easily, with a relatively small engine. And it shouldn't be very expensive. Look at trawlers! The sticking point is running for shelter at 15 knots. That requires a semi-planing hull, a bigger engine, and perhaps twice the cost. Take your choice. In the Mediterranean, I would be happy with the comfy slower choice.

 

You have a few conflicting issues in your wish list. Lots of volume and fuel efficiency generally don't mix, unless you accept the volume being stretched out fore and aft. Big butted boats don't do well in a following sea or offer as much internal volume. A round bilge will offer a softer ride, assuming some deadrise, but a hard chine will make a more stable platform.

 

I thought you would have seen iit on the nigel irens website.- same designer as the 62fter I linked "just for you". http://www.nigelirens.com/boats/power-boats/rangeboat

Sustained 14kts cruise requires 80hp from the engine. At this speed that equates to 17L per hour, 1.2L per NM. If you slow her down to 8kts I'd expect at least twice that efficiency. Considering she has a 200hp diesel installed, sprint speed should be up around 20kts.

 

The Mainship 34 was based on lobster boat design. With 200 HP this boat could plane at 15knts and liked to run with the forefoot just a little bow high at 8-9 knots.
Many of these are being repowered with a little more HP and finding that at about 17-18 knts the keel makes handling a little squirrelly. The deep forefoot can cause some serious bow steer too, otherwise as noted these hulls a pretty kind

 

The low price of second hand displ. Boats is a reflection of the demand for s/d boats that can at least max out in the low teens.

When you think that an average 250hp diesel can happily purr along at 1500revs burning 1.5gals an hour/8kts' and then be opened up to max out at over 3000 revs/15kts in a 8 ton hull, you have a lot of options in a s/d hull.

Chugging along at slow speed makes Displ. Hulls very restrictive.

 

Those figures seem nearly too good to be true.

I'm finding it hard to find a 38' boat that light to compare it too, but the Merry fisher 925 weighs 4.6 tons and with 250hp at 2600revs/ 36 ltrs/15 kts......twice as much fuel.

So the Range boat is twice as efficient as a conventional s/d design of the same displ?

Really?

 

Thanks for a very clear explanation of the lobster boat characteristics!

My real interest was 'would a lobster boat hull' make a good choice for a cruising boat?

The Mainship mk1 is one of my favourite boats.

 

>When you think that an average 250hp diesel can happily purr along at 1500revs burning 1.5gals an hour/8kts' and then be opened up to max out at over 3000 revs/15kts in a 8 ton hull, you have a lot of options in a s/d hull.<

However operating a 250 hp rated engine at 1/10 its rating may reduce the service life by half or more.

No big deal as a good diesel might make 8000 hours , so reducing it to 4000 before wet stacking would be fine for a 200 hour a year boater.

4000 hours at 200 a year is decades.

The closer the diesel is to an automotive or light truck engine , the less this is a hassle.

The closer it is to a heavy duty , industrial rated engine the more minor load hassles there are.