Moderate Speed... Any Weather

Tri-star - you're taking this WAY too seriously. Nobody's having a go at you, we're just interested in your so-called wonder boat. And if the design is so basic that we are able to 'splash' it from a couple of photo's, then there's nothing so wonderous about it anyway....

Tom - bridegedeck clearance is just one of the variables that can contribute to, or eliminate, slamming. Much reading has lead me to the conclusion that a minimum of 900mm (and preferably more) is needed to minimise it. But of course this depends very much on the rest of the design and the sea-state where the boat is to be used. At the end of the day, I guess it's somewhat subjective. I've spent days out fishing in smaller (up to 28ft) planing powercats. I hate them. Sure they're fine once they're up and going, but slow down and it's nothing but thump, thimp, thump.

Which brings me to Alex's comment -

This is only the case for planing catamarans. The displacement cat will not rise percepatably at speed, as there is very little contribution from dynamic lift

 

Will, I'm never going to get very deeply into powercats or sailing cats for that matter. I do like the speed sensation once in a while but I'm one of the throwbacks that actually likes a sailboat to heel a bit. The feel of a good boat knifing to windward in a good breeze with the rail near down does something that even more speed in a multi just doesn't match for me. I do recognize the great advantages of multis for some uses though. You Aussies do build some very impressive big displacement wave piercer cats. I assume they can make them with bridge decks high enough to avoid the mentioned problems.

 

Yes and no. I remember quite clearly when one of the early wave-piercing Inact ferries ran into the back of a wave and came to a very abrupy halt. It ripped the furniture off its mounts and sent it flying up against the front of the vessel. The bar nearly killed the owner of the company.
They were very different beast back then. Nowadays the centre hull resembles a very deep forefooted monohull, with a pair of wave-piercing hulls tacked on either side. I still have reservations about their suitability in anything much more than surface slop though - even though one held the blue-ribband trophy for some time.

 

My last post was in reference to a planing cat, but one displacement cat I'm considering is the "Eko-Kat" built by Multi Marine (not the Aussie one). The building technique lends itself well to increasing freeboard so that this could be made with seagoing under-deck clearance. Keep in mind that I would build a considerably different supstructure.



For more images go to Multi Marine at: http://www.multimarine.com/boat_sales.html

Click on used boats, then "Eko-Kat".

This boat would get very good gas mileage. The builder quoted me 20mph with 30hp @ 12 mpg. Even accounting for seller's bias, this is an economical boat.

~ ALowell

 

Well I had hoped the thread would go a little further on the subject of moderate speed and rough water.

It seems that alowell has decided on a little powercat. I have no experience with these, but from what I understand they are very smooth riding in choppy water. But once you get past the chop and into rough rolling water, that may be a different story.
Correct me if I am wrong, but don't these power cats go back about 50 years to the hickman sea sled.
Most designs do better in the type of water they where designed for, local designs for local waters.
It still is a matter of how rough of water and at what speed.
Of course full dissplacemnet hulls are going to handle the roughest water and give the best ride, but at low speeds.
That is where I have becamed a fan of the semi- hulls, old time launches that run in the mid to upper teens and maybe low 20's depending on the length of the hull. A revival of the launch, that was replaced by the modern high speed planning hull..bang, bang bang...

Then again what about a boat such as the pulsifer hampton...
about 14 m.p.h. top speed. Is that too slow? For rough water capability.

 

With you there, Tom. Recreational boating, like all recreation, is about creating experiences that appeal to us.

Charlie

 

ALowell,

The Eko-Kat appears to be an excellent choice for calm water and chops. Performance might not be exaggerated; look at the Pulsifer Hampton performance quoted for a heavier monohull, the two speed figures seem consistent. If each boat were sold with an attractive woman as shown in photo 7, it would become one of the world's most popular designs!

Rough water, to me, is when things start to get out of hand, as in crossing a bar with an outgoing tide and onshore wind, or any situation in which the wind is 20 mph or more and has had a long fetch, as in easterly or NE winds on the Atlantic. I'm not a designer, but I have driven boats into steep seas many times, and here is where I see shortcomings. I can see those twin hulls knifing into a sea without generating much lift, and the bridge taking the full impact. If you decide to use this as a basis for your own build, I'd be sure to extend that small center hull quite a bit, if you intend going offshore.

Charlie

 

Tri - star,

OK, from your statements above, it sounds like you're certain you've been the victim of having your design stolen, appropriated, or, like a friend of mine, had a client take preliminary renderings contracted for, hire a student draftsman to complete them, and refuse to pay on the grounds that, "you didn't give us what we wanted, so we don't have to pay you. We "had to" hire the other/cheaper guy to get it as we wanted. If you don't like it, sue us. Our 10 lawyers will be happy to meet your 1 in court.......". Personally, I've had the experience of not being paid by a client for industrial recycling equipment I designed. So yes, I do understand that experience. It sucks.

I understand your reluctance to give too much info. Go back and review; you'll see that I never challenged your performance claims. I did challenge your method of communication, because you're challenging others without giving any data to support your claims. Since you've sold your design to customers who are satisfied, it must be a good design. All I am saying is that coming into a forum, claiming you know more than others without giving any supporting infomation, doesn't accomplish anything.

Earlier I posted a link to the builder of Erie Cats in response to a question posed by ALowell. I don't know that builder, but, from the information he's given, the design looks sound, and performs well in the video. You say you've been designing a good powercat for about 18 years. That's great. As I'm sure you know, Albert Hickman's sea sleds were first designed before WW I. They performed well in rough seas, and the early Boston Whalers were inspired by Hickman's work.

As Will said, if a glimpse of some photos is enough for someone to copy your work...... On the other hand, you're exposed already, unless your fisherman clients are never seen by others, never talk about their boats over a beer, and keep them hidden away in locked sheds in hidden harbors when not in use.

Some comments about why your design works better, even a photo or two, shouldn't hurt you, and may do well in spreading interest in your work. ALowell seems to be serious about building from a proven design that meets his needs. Perhaps he'll end up buying your design.

Welcome to the forum. I've found that people here are, for the most part, sincerely interested in learning more about optimal boats for various purposes. Try not to be overly sensitive about comments made. Like you, there are others here who have earned their knowledge through hard experience, and they want to defend their ideas. The result, of the interchange, hopefully, is that we all learn more, and use the knowledge to improve the boating experience for everyone.

Best,

Charlie

 

Ron,

Pulsifer's Hampton seems to embody much of the elements of the East Coast sea skiffs. The lines remind me of the wood hull Pacemaker I described earlier in this thread. I can speak from experience that that design handled rough seas very well (mostly "landlubber" passengers falling asleep while we progressed through steep 6-8' seas one day says something for the easy motion, I think), and planed with moderate power in the 14- 20 mph range. Apart from offshore racers (and even they slow in rough seas, with races called off if it gets "too rough") no one tries to maintain high speeds in truly rough seas. 14 mph would be the upper end of speed for any hull type in heavy seas. The Hampton design does seem to address what ALowell posted at the beginning of this thread.

Charlie

 

Another design to be considered is Loveofsea's flat bottom skiff. Since it's description and photos have been published on the Internet and in a magazine, I'll just link to that. He makes some interesting claims, and describes why he believes his design handles rough seas. Since he goes offshore regularly in this boat that he built himself, his ideas are worth reading:

http://www.oceanskiffjournal.com/SubscriberContent/Articles/Vol02Issue01/General/BoatProfile3.aspx

 

I think the Pulsifer Hampton might be a good concept, however it would need to be scaled up for my purposes as the normal 20' version has very low freeboard and doesn't look like something I would want to be in during any kind of survival situation.

Everyone seems very taken with the idea of the Hickman Sea Sled. I've never been convinced about their ride characteristics, though I've never ridden in one so I don't speak from experience. One thing that worries me is that the claims made about Sea Sleds may be out of date. If the claims people often site are in comparison to the boats of the same time period - before the advent of the deep vee - what was considered good performance then might today be surpassed by modern vessels. This is just conjecture on my part so please correct me if I'm wrong. I would be very interested if anyone has personal experience with an inverted vee boat.

I apologize for not posting drawings of my catamaran design. I'm not worried about plagiarism (as seems to be popular), I just can't get my pdf files to download from my hotmail account. In the meantime just imagine a cat about 20' long, 4' high freeboard, 2' wide hulls, about 15 degrees of vee and the deck at gunwhale level to preserve under-deck clearance. This doesn't allow for any accomodations or even seats, but would suffice for a console and railings.

~` ALowell

 

ALowell,

That's a good point. The guy we both mentioned earlier in this thread, Ken Handman, is designing the Port Erie Cat now, and he has stated that he owed a lot to Hickman and the sea sled. His site has photos and videos of the boat running. I believe the sea sled concept is sound. More validation comes from the fact that Raymond Hunt used the sea sled as the basis for his design of the original Boston Whaler. The difference in performance won't be as dramatic as it was in Hickman's day, but I suppose that's simply because powerboat design has made a lot of progress since 1912.

I was driving back from an errand this afternoon, and passed a boatyard with some powercats out of the water. I noticed that they had some of what you've mentioned, i.e. narrower beam than sailing cats, high freeboard, and a vee section center "hull" obviously designed to limit slamming. Not the prettiest boat I've seen, but it looks like it would perform well in rough seas. If your heart's set on a cat, your own ideas, similar to what I saw, seem pretty solid.

 

ALowell, after all this discussion, I'm still not quite clear as to the intended use - though I suspect it's as a Martha's Vineyard commuter... but then why the speed requirement in heavier weather? Seems like the ferry backup would cover you there.

Can you elaborate a bit on your specific requirements, and why your Eastern(s) and Duffy won't do?

Sal's Dad (learned to sail on Buzzard's Bay)

 

It will be primarily used around the Cape and Islands for travel to Nantucket and the Vineyard. The ferry would do just fine, but what's the fun in that? Really I hope to convert my design, if it's proven to work, for cruising around the east coast.

My Eastern 18 is a wonderful boat and I can't say enough good things about it. However, at 18' it's not going to be safe for any really exciting weather. The Duffy mentioned in my profile is actually my uncle's. It is quite efficient and has lots of room, but unfortunately it's not my boat.

I have finally been able to upload some drawings of what I have so far. Please excuse the crudeness of the drawings -- I don't have access to any CADs.

 

I think you did a real good job on drawing the little man.
As for the boat, it looks as if you will be on it and not in it, not good for rough water. It looks as if you only have less then knee deep on the sides, would be easy for someone to get tossed overboard.