What's the best shape for a fast & efficient catamaran hull?...

[Seagem]

MC29: Cat Mono Hybrid...



Interesting design that needs refining, judging by the amount of spray thrown under way...

The lay-out barely meets requirements, even though there is no access into the hulls and the beam is only 8'6"...



http://www.aviadesign.com/MC29/MC29B...let%20size.pdf

[Seagem]

New thinking in cat design from Glacier Bay founder...

http://www.aspenpowercatamarans.com/pages/Welcome.html



Specs and lay-out: http://www.aspenpowercatamarans.com/...AspenC-80.html

I'm not keen on a single diesel, as handling a cat with a single engine mounted in one hull in tight quarters is a serious pain. However, these drawings show an interesting lay-out, including a king size berth, full height head, full size dinette that could convert into a double berth and reasonable size galley all in a compact 26' cat, plus swim platform...

Tunnel height, overall beam and lay-out are suitable and it has asymmetric hulls that may bank inside in a fast turn: I can't see why twin outboards could not be substituted to the single diesel engine...

Test Boat: 26' engineering proof of concept test hull - no deck, running at 18-24 mph, hands off wheel, burning 2.4 to 3.8 gph with Yanmar 110 hp...



Full size photos of Test Boat: http://www.aspenpowercatamarans.com/...photoPage.html

However, the hulls configuration is actually that of a proa with a much narrower port hull, which might not lend itself too well to twin outboard power, except perhaps, where a 150HP outboard is used on the main hull and a get home kicker on the other: steering in close quarters would also be much improved...

It takes a lot of guts to bring out such radical designs - there are also a 39' and 48 footer - in such dire economic times...

[h2otaxi]

Originally Posted by mark775

There is a Chilkat thing here and the owner loves it but the outboards are ripping the the back of the boat off... Most in this neck of the woods have given up on little cats that plane, by the way because of the hobby-horsing and general thrashing.

I own that Chilkat in Homer. The transom is sound. This boat has been put through the rigors. I trust it and my clients prefer it. It is a comfortable ride in some of the most severe conditions. The Chilkat cruises at 30kts at 4000rpms and consumes 9.5 gallons per hour with Honda 225s. We are seeing more small cats on the Bay every year. Comfort AND efficiency rule the day.

[Seagem]

Originally Posted by h2otaxi

I own that Chilkat in Homer. The transom is sound. This boat has been put through the rigors. I trust it and my clients prefer it. It is a comfortable ride in some of the most severe conditions. The Chilkat cruises at 30kts at 4000rpms and consumes 9.5 gallons per hour with Honda 225s. We are seeing more small cats on the Bay every year. Comfort AND efficiency rule the day.

Glad to hear from a happy Chilkat owner, as it seems to be one of the most successful design reviewed so far: certainly, the cruising revs fuel efficiency at 3 miles per gallon at 30 knots is nothing short of exceptional...

My only concern however is the low bridge deck, the slope of which is fairly blunt forward, as we operate in open Caribbean waters with no land protection: once it's too rough to get on the plane, then the ride should be rather noisy from the slapping on the bridge deck and probably uncomfortable...

[blackfeather]

Originally Posted by mark775

There is a Chilkat thing here and the owner loves it but the outboards are ripping the the back of the boat off... Most in this neck of the woods have given up on little cats that plane, by the way because of the hobby-horsing and general thrashing.

I have to ask this poster where he gets his information. I have been on the phone with the owner of this vessel and his marine surveyor - neither has indicated that there is any structural problem with the transoms on this ChilKat. I built that ChilKat. The laminate schedule in the transoms is as follows: gel coat, 1.5 oz CSM for skin coat, 2408 ELTM, 2408 EBXM, 1.5oz CFM, (2) 1/2" 24lb fiber reinforced urethane foam with another 1.5 oz CFM down the neutral axis - not for stiffening but rather to ensure flow during the infusion, then another 1.5 oz CFM, another 2408 EBXM and finally a 2408 ELTM. The core is tapered, and all of the overlaps are staggered and effectively doubled up. It was infused at 28" of mercury with vinylester resin. If you run the transom through a laminate analysis you will find that it easily should hold up under those engines. The cap and the motor well is joined to the hull with Plexus MA 590, and all the seams are hand taped with 6" and 8" biaxial for redundancy. I have a hard time believing your assertion. I further have a hard time believing that you have been for a ride on this boat. It does not hobby horse or thrash - and I speak from the experience of driving this design out on the Gulf of Alaska in 13 - 15' seas with a good 2' chop over the top of them, down Chatham straights in 8' seas on a 3 second period (an uncomfortable ride at best in any 30' boat) as well as in countless other conditions. It is true that this design does get some tunnel slap in very specific conditions - however it is not a regular phenomenon and one must realize that what offsets this is the developed "air cushion" which sits in the tunnel at effectively any speed over 15 knots creating what is generally a very comfortable ride. All designs are a series of trade offs. There is no perfect boat, no perfect hull shape.
Seagem, in direct response to the topic which originally started this thread I would say that the best derived design really depends on your stated operational envelope. Then keep the cat as absolutely light as possible. Efficiency is directly relational to weight, and these days it seems that everyone wants to cram as much as possible into a small vessel - that is the chief detractor from performance.

[Seagem]

I have no doubt that your boat is well built and that if any problem had arisen in the first one constructed, it would have been corrected in subsequent editions...

Everything I have listed, including 10' beam and high bridge deck, can be done in a small package - that may have to be extended to 28' in length, which is fine by me - and it has already been done by none other than the famed previous owner of Glacier Bay in a 26' boat, which is unfortunately a single diesel PROA!!!...

http://www.aspenpowercatamarans.com/...AspenC-80.html

Don't forget to take the 360 degree tour of the accommodation mock up...

Originally Posted by blackfeather

I have to ask this poster where he gets his information. I have been on the phone with the owner of this vessel and his marine surveyor - neither has indicated that there is any structural problem with the transoms on this ChilKat. I built that ChilKat. The laminate schedule in the transoms is as follows: gel coat, 1.5 oz CSM for skin coat, 2408 ELTM, 2408 EBXM, 1.5oz CFM, (2) 1/2" 24lb fiber reinforced urethane foam with another 1.5 oz CFM down the neutral axis - not for stiffening but rather to ensure flow during the infusion, then another 1.5 oz CFM, another 2408 EBXM and finally a 2408 ELTM. The core is tapered, and all of the overlaps are staggered and effectively doubled up. It was infused at 28" of mercury with vinylester resin. If you run the transom through a laminate analysis you will find that it easily should hold up under those engines. The cap and the motor well is joined to the hull with Plexus MA 590, and all the seams are hand taped with 6" and 8" biaxial for redundancy. I have a hard time believing your assertion. I further have a hard time believing that you have been for a ride on this boat. It does not hobby horse or thrash - and I speak from the experience of driving this design out on the Gulf of Alaska in 13 - 15' seas with a good 2' chop over the top of them, down Chatham straights in 8' seas on a 3 second period (an uncomfortable ride at best in any 30' boat) as well as in countless other conditions. It is true that this design does get some tunnel slap in very specific conditions - however it is not a regular phenomenon and one must realize that what offsets this is the developed "air cushion" which sits in the tunnel at effectively any speed over 15 knots creating what is generally a very comfortable ride. All designs are a series of trade offs. There is no perfect boat, no perfect hull shape.
Seagem, in direct response to the topic which originally started this thread I would say that the best derived design really depends on your stated operational envelope. Then keep the cat as absolutely light as possible. Efficiency is directly relational to weight, and these days it seems that everyone wants to cram as much as possible into a small vessel - that is the chief detractor from performance.

[billberit]

http://www.ecocats.com/8mChaseboat/t...1/Default.aspx

These guys have it close to what would work in the Florida Keys.

A 22 to 24 x 8 to 9 beam and shallow draft hulls of 8 inches or less, a fat cutwater, and ballanced level no matter what engines you stick on her.

Light weight and stable. T Top or full overhead

B

[simon full bar]

We have just lauched a range of catamarans that are very efficient and sea kindly further details at our web site fullbarcomposite.com
We are currently developing a 9.9m model for the UK fishing industry.
I will post further details this evening
Cheers Simon