New Long Thin, Hyper-Efficient Trawler

Rusty

The FPB designers, owners and builder are not aware of your oft mentioned "pitching problem" I will say though that in short period 8+ foot seas many fat body vessels I've been on - pitch. Seems that all boats do, in fact I saw a video of a tanker, oh what the heck.

On a different note, I recently talked with one of the Black Swan guys, it is moving ahead. Learned a bit about their plans, hopes and dreams. Smart group.

makobuilders said:

Perhaps the motion is exasperated by the wide stern with too much buoyancy? I haven't heard stories of the traditional (early 1900's) narrow double ended trollers pitching like what we've seen in the video.

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Double ended longline trollers although they are quite slim in comparison to conventional trawlers, are still way off the super slim streched out hull of the Dashew. In fact the Troller would be considered a traditional shaped boat in comparison to the FPD , so it should behave just like a conventional boat in the pitching department .

I would classify the Dashew type boat as an 'extreme' example of its design class.

sunchaser said:

Rusty

The FPB designers, owners and builder are not aware of your oft mentioned "pitching problem" I will say though that in short period 8+ foot seas many fat body vessels I've been on - pitch. Seems that all boats do, in fact I saw a video of a tanker, oh what the heck.

On a different note, I recently talked with one of the Black Swan guys, it is moving ahead. Learned a bit about their plans, hopes and dreams. Smart group.

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If you had just spent $M's on a new boat, would devalue your investment by admitting the design was deeply flawed? I'll try and dig up the magazine article that went with the MBY test video . Even though Dashew took advertising space, the review made some very cutting remarks about the handling of the boat.

This is well know trait in trimarans which have a 'monohull type' central hull located between two small outrigger floats.

I respectfully refer you back to this article by a professional NA...

http://www.graingerdesigns.net/the-lab/optimising-hull-lines-for-performance/#

sunchaser said:

Rusty

The FPB designers, owners and builder are not aware of your oft mentioned "pitching problem" I will say though that in short period 8+ foot seas many fat body vessels I've been on - pitch. Seems that all boats do, in fact I saw a video of a tanker...oh what the heck...

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I tend to agree. I think she was cruising really quite flat in the second video, and in the first, considering the speed she was going and the severity of the seaway, chosen deliberately to test speed in nasty stuff, (taken off Auckland, I think, where she was made), the pitching while definitely occurring, would not have felt that bad where the crew are stationed.

You need to take into account she was built purposely with light ends, with most mass in the centre, which is where the crew are also. The pitching then rotates round that centre of mass so as to reduce high speed pounding in the ends, when the sea state and speed overcome her slice through the waves ability. Works a bit like the way that rolling is less noticeable the lower in the boat one goes, so nearer to the centre of lateral rotation. That's my take on her anyway.

Rusty

Dashew's website encourages Q and A. I will watch there for your questions and comments to Steve on the article you reference and "pitching problem."

"There are all kinds of tradeoffs in yacht design. One of the most difficult to get right is the relationship between hull shape at the waterline and further up the topsides. If you are too fat at the waterline, the boat pitches and rolls uncomfortably. If you are too skinny, then a variety of unhappy things may occur. When you are going downhill at speed, more volume in the ends is desirable. Heading into the waves the opposite is the case, until you encounter large, breaking seas, in which case you need sufficient volume above the waterline so that the bow lifts to the oncoming wave.

Of course too much lift and a dreadful pitching or hobby horsing ensues with a substantial reduction in speed".

SetSail FPB » Blog Archive » Survival Storm Tactic Tested Off The Needles In Breaking Seas: Updated With Video

FPB 78 Hull design analysis

Our Long-cours 62

Rustybarge said:

Maybe that's why nobody but Dashew and one other yard is building these hulls; super economical in flat water, a nightmare in rough conditions .

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Was even more economical than the Dashew but we NEVER had this type of "problems" luckily because my stomach will not survive