Asymmetrical+Foil vs Symmetrical Multi

[skypoke]

I'm evaluating designs for a 30' outboard powered alloy hard chine powercat. The choices are narrowed down to two, one is a foil assisted asymmetric hulled craft, the other is a more conventional symmetrical hull. Sea conditions for operation are typically "squared up", 3-5' seas, 3-5 second period. This is a fishing boat. Typically, a 35 mile minimum run is required one way. My goal is a craft which will comfortably make the run at good speeds without excessive pounding and discomfort. Naturally it needs to be able to handle conditions in excess of the above, but these are typical ranges.

The designer of the symmetrical hulled craft maintains that while foil assisted craft are exhilarating to run, the more conventional craft will outperform it in real world conditions. He states sensitivity to trim, loading, side loads make them tricky to operate. He also indicates that the foil will be detrimental when sea states build to a point where throttling back is necessary.

Both designers are well respected, experienced in multihulls. In seeking to educate myself I'm finding lots of conflicting reports on the merits of these hullforms. I want to build state of the art, the most evolved design possible and am comfortable with the added cost and complexity of the foil if it will truly provide benefits in the form of speed, sea keeping, fuel efficiency. Would appreciate your thoughts on these issues.

[KCook]

I don't have anything to contribute. But this is certainly an intriguing project! If I may, I have a few questions -

I assume that squared up seas means steep faced? Are swells also a factor in your waters?

Nice descriptions of the two proposals. But it would be nice to see what we are talking about. Any chance of posting sketches of these, or a link to another server with sketches?

Always curious,
Kelly Cook

[brian eiland]

You owe yourself some time looking at all of the info on the Hysucat foil systems utilzed with asymmetrical hulls. By far the most simple and very effective....and look at there RIB adaptation

Start with http://www.sun.ac.za/kie/unistel/tec...s/foiltech.htm

[skypoke]

Kcook, thanks for your reply. "Squared up seas" means that the period between waves is equal to wave height. In other words, brutal chop. This is typical here, Texas coast. While I haven't had the pleasure of operating in the long rolling swell conditions like off the Pacific coast, I imagine that these would be much more friendly to ply, unfortunately for me those are the conditions that many cat designs are tested and run in. Not many of these craft around here.

I would like to post design info, but since these are the property of the respective N.A.s, I would need to get permission to do this first. While I have entered into preliminary design agreements, I would be loath to ask until I have made a firm committment to final design. What I am seeking to do through this forum is to increase my knowledge base to the point of being able to ask intelligent, pertinent questions of these designers. Being self employed myself I'm pretty sensitive to the amount of time that can be invested in preliminary dealings with prospective customers. Lord only knows how many well intentioned dreamers these guys deal with.

In this case, however, I'm committed and funded for this build. It's a tough decision. Regards, Chuck.

[skypoke]

Brian, great site, thanks. Most telling to me was Makaira, 8.5 M, 9K lbs, 40 knots with twin 150's. This is a boat with significant superstructure, assuming it's not some kind of flat hulled design we're looking at a pretty efficient boat. I wish, though, that there was some evaluation of ride and handling.

It looks like 40 knots is near the limit of a submerged foil. There's quite a few cats that can hit this speed without benefit of foil assist but it comes down to a question of HP necessary to attain this speed. Kind of like the old flying axoim, "put enough power on a barn door and she'll fly." But 40 K is more than enough, I'd like to be able to make 25 good through seas without constant throttle jockeying and a back brace.

Foils aside, any opinions on the ride qualities of asymmetric vs symmetric hulls? I know the asym has a higher speed potential and also leans into a turn. Is there a price to pay in additional G's coming off waves?

By the way, I had previously attempted to contact Boatloft about available designs/services to no avail. Guess they're too busy...

Rgds, C.

[KCook]

Once vacationed in Galveston. Loved it there! The chop back on Galveston Bay certainly was the steepest s**t I have ever experienced

Offshore cats are NOT my expertise. But this is fun to learn about. I assume symmetrical vs asymmetrical is whether the V on the bottom of the sponson is centered (symmetrical) or offset toward the inside (asymmetrical)? If so, all of the high performance planing cats I have seen have been asymmetrical. Unless you count the flat bottom ones as "symmetrical". I thought the symmetrical designs were limited to displacement or semi-displacement cruising models?

The foil solution is intriguing. Can that designer hook you up with owners of his boats for a demo ride?

Just sputtering here,
Kelly

[skypoke]

I've decided. It's to be an asymmetrical hull, foil assisted cat. Thanks to the link provided by Bryan to the Unistel site, I've finally found the information I need in the form of publications by the developer of the foil system, Mr. Hoppe. Finally, some hard data as opposed to advertising fluff.

Considering risk of building relatively new technology, I look at it like this. I could take the safe route and follow convention, ending up with a moderately performing hullform similar to the thousands- nay millions of craft out there, the very ones whose perfomance, or lack of it, infuriates me on a regular basis. I'm sick of feeling like I'm pushing a hole through the water and incidentally following it. There has got to be a better way.

Am in contact with Gunter Hoppe at Foil Assisted Ship Technologies. Will keep you posted on progress. Thanks to all who have assisted in the search for information.

Regards, Chuck

[brian eiland]

Foil assisted RIB

I'm assuming you also found this site,

http://www.hydrofoildesign.com/media...cation2Web.htm

which is a little closer to the size vessel you were contemplating

[badges65]

Have you looked at these Hulls
http://invertedvboats.bravepages.com/
they will outperform most and only use one motor with a minimum of 20% less power
don

[skypoke]

As a matter of fact I have looked at the inverted V craft, seems like the design fell by the wayside after some rather spectacular early successes. I talked with Bill Lincoln about this style, Winninghoff Boats built several of them in the 40' plus range with good performance. After thinking it over I decided the multihull was more to my liking even though the IVV posts some impressive performance. The fact that it becomes essentially a flat bottomed boat aft gives me pause. Now if I was wanting to transport heavy loads at high speeds inshore....

But it may be that the Hickman style is the overlooked silver bullet. Certainly intriguing though I understand that tank tests vs. V bottom are not convincing. Chuck

[KCook]

That "inverted V" looks like an attempt at air entrapment to me. Frankly, I find a conventional tunnel hull a lot more persuasive. Here is a photo of a 26 footer . Admittedly, this one is to small for big waves offshore. Of course these air entrapment designs have just two speeds - putt putt or full bore!

Kelly

[badges65]

Hi,
It is obvious that neither of you have looked at the hull properly and have never had experience with it ..
i have had that 6.5M hull in seas which have forced other boats with much more power to slow down and i have never been in a hull which has given me more sense of safety at sea.
the biggest problem with the hull is OPERATOR COMPLACITY!!!!!!!!!!
You will find the hull we have is a variation of the sea sled but quite a few different aspects as with winninghoff they just converted one of their cats to a ivb..
don

[skypoke]

You're right about one thing, I've never seen one of these hulls, even after living on the coast for years. As far as looking at it properly, well who's to say? But at some point you have to "freeze the design", make a decision about which way, out of many possible directions, you're going to go. Is it possible to make an absolutely optimal decision? Questionable. Fact is, I could spend the rest of my life in a comparison of various hullforms without determining the absolute best cause they're all compromise. But for me the foil assisted cat is looking pretty good. Chuck

[brian eiland]

Originally Posted by skypoke

I've decided. It's to be an asymmetrical hull, foil assisted cat. Thanks to the link provided by Bryan to the Unistel site, I've finally found the information I need in the form of publications by the developer of the foil system, Mr. Hoppe. Finally, some hard data as opposed to advertising fluff. Am in contact with Gunter Hoppe at Foil Assisted Ship Technologies.

Will keep you posted on progress. Thanks to all who have assisted in the search for information.

Regards, Chuck

Just wondering about your progress on this project??