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Old 04-20-2013, 03:13 AM   #1
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Interesting hull form

I have never seen a hull form like this...one of the most unusual ones I've seen....not for it's shape b/c that is normal enough, but for the ridges the hull has on it. I can only imagine how much more a bottom job for that boat costs! Anyone ever seen this before?








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Old 04-20-2013, 04:55 AM   #2
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It looks like it might be reinforced for ice conditions.
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Old 04-20-2013, 06:35 AM   #3
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I would have thought more for rigidity, semi-planing, and less spray while at speed. If it was for ice, I would expect the props to be better protected, but they are just standard twin prop set-up.
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Old 04-20-2013, 08:20 AM   #4
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Well, whatever it is, it must be strong as all get-out, and I can't imagine it was cheap to do it. Yanking that thing from the mold must have been a bit different as well. Interesting.
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Old 04-20-2013, 10:10 AM   #5
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It may be designed to draw aerated water under the stern, increasing top speed.
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Old 04-20-2013, 10:28 AM   #6
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OK, this is reaching into the back recesses of my brain, but I believe that you are looking at a hull from Halmatic in England, originally designed for patrol boats. I think that in the last days of existence Owens finished a few of these hulls in the US.

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Old 04-20-2013, 10:31 AM   #7
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Quote:
Originally Posted by Peter B View Post
I would have thought more for rigidity, semi-planing, and less spray while at speed. If it was for ice, I would expect the props to be better protected, but they are just standard twin prop set-up.
You're right. On second look the strakes don't look like they'd do much for ice protection.
Sure wouldn't want to do a deep blister repair on that hull.
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Old 04-20-2013, 10:50 AM   #8
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This is a bad design. Not unsafe or anything like that but just very inefficient. All those pleats in the hull are supposed to be lifting strakes but very poorly conceived. Most boats w lifting strakes terminate the strakes just aft of amidships to minimize wetted surface and drag. Most designers minimize deadrise so-as not to loose too much efficiency. Most designers minimize the size and number of strakes to minimize wetted surface and drag. Those that employ strakes as spray rails terminate them just under the WL at speed to minimize drag.

That said this boat looks like it was designed to maximize drag. I'm almost sure the designer was not an idiot (definitely not though) and had an agenda that did NOT include efficiency. He was probably designing a custom boat and the customer said something like "I don't care how inefficient it is I want the smoothest ride I can get and I want it in 10' seas". The designer may not have told him he'd never be able to sell the boat as he probably wanted the job but he could have argued at great length to not get his name on the design. That may not have been ALL bad as it's a better looking boat than most. This boat would have been a hot seller compared to the only boat I designed and such is the world of one off boats. One seldom gets a boat extremely good at one thing as too many compromises must be made to get there.

This boat is either very slow and thus should be a FD hull or it has HUGE engines and burns fuel like a B-29. But I like it's looks. The grooves, pleats, strakes look a bit like the business end of of a whale.

Now that I look at the pics again I see it's not a full planing hull but a bit of a semi-disp hull. Just a bit though. And it dosn't have big enough props to consume huge amounts of power.

I don't think ice or aerated water was in anybody's plans but Mr Welch has probably opened the mystery box. Patrol boat. Government money to build and operate it. I have a distant recollection of other boats from England that looked much like this one. The offshore racing boat Tramontana looked a bit like this and was powered by (as I recall) four Jaguars. The Tramontana had a much more efficient and traditional warped hull than this (assumed) patrol boat. I personally still view it as a poor design. Having said that I may need to hide behind a tree when someone like TAD Roberts comes along and shows what a brilliant design it was/is.

However I do wish we had a post of a hull as unusual and interesting as this one every day.
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Old 04-20-2013, 10:52 AM   #9
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Anybody remember lap strake hulls? My worst job in a boatyard was (RE)painting a Chris Craft to perfection using Pettit enamel paint and a very demanding owner.

This hull can't decide if it is deep V, SD or displacement. Must be from the late 70s. Very nicely kept it would appear, which more than makes up for its oddity IMHO.
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Old 04-20-2013, 11:06 AM   #10
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Quote:
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Anybody remember lap strake hulls?
When I was just a pup, my uncle had a Lyman. (heavy)

(Not my Uncle's boat)
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Old 04-20-2013, 11:06 AM   #11
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Many go really fast boats have steps across the hull to break the water adhesive to the hull creating vacomm pockets so the boat can go faster. Our run about has a step. however steps run the length of the hull would work also.
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Old 04-20-2013, 11:11 AM   #12
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It appears the top of the chamfers are parallel with the water line and my guess is it was a design intended to increase lift. Some mid eighties Bayliners had a hull with 4 hull steps that they called a quadralift hull. I don't know about sail boats but it wouldn't be for aeration on a power boat, the denser the water the greater the bite your props get. Aeration is the bane of power boats in many ways, ever follow directly behind another boat or notice the dramatic loss of planing speed in very shallow water, this is because of the higher content of air in the water. Cavitation around the props is a whole other issue.
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Old 04-20-2013, 11:27 AM   #13
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I know very little about hull design, but with my last planing hull I noticed a higher speed travelling over "rippled" water at a given rpm, in comparison to water which was glassy smooth.
Would this not be due to less water/hull contact area due to the increased air content under the stern?
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Old 04-20-2013, 12:41 PM   #14
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"Wetted surface" was the first thought coming to mind.
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Old 04-20-2013, 12:50 PM   #15
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I have seen similar hulls used on high speed patrol and off shore pilot boats but they employed much larger running gear.
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Old 04-20-2013, 01:43 PM   #16
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That is an interesting hull design. I think the "strakes" are an attempt to create a semi-displacement hull form while maintaining a more traditional full displacement hull shape. It is soft-chined the full length of the hull and the "V" is carried all the way to the stern. That is an amazingly deep V at the stern, even the famous "Carolina" deep Vs are about 24 degree deadrise at the stern, that looks more than that. Most semi-D hulls harden the chine from about midships back and the stern sections flatten out to create lift. I wonder how effective those "strakes" are. As Eric noted, it probably needs a pretty substantial powerplant to get is moving past hull speed. Also, I don't see any stabilizers, I would guess it is a pretty rolly boat. Since none of us seems to have seen similar hull forms, one has to assume it was not a spectacularly successful design or everyone would be doing it. Maybe if Tad sees this he can chime in and give us a better explanation.
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Old 04-20-2013, 01:47 PM   #17
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I think this is a British John Teal design which he discused in some detail in one of his books. Looks like it would nearly double the wetted surface but actually reduces it at planing speeds by having a spray rail and lifting stake for every condition of sea and speed. Or so his theory went.
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Old 04-20-2013, 02:15 PM   #18
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Well, by conventional current naval architectural thinking this would be a mistake, or someone trying to fix a mistake by making another. Who knows what the thinking might be, but the result would be minimal, if any. The upper one or two strakes might keep the bow wave from shooting up the topsides and landing in the skipper's face, but that's about it.

I don't think it's one of the early Halmatic hulls Scott, the round version they used had a spray flat in the topsides above waterline. But it may be a variation thereof.

Tramontana was a warped bottom 40' that won the 1962 International Offshore Powerboat Race. She was designed by Commander Peter Du Cane (Vospers) and powered by a pair of monster Italian CRM's, something like 1150HP each. She supposedly went over 50knots. She had no lifting strakes on her bottom. Sonni Levi's boat's of the 1960's, Merry-Go-Round (Sir Max Atkin) and A Speranziella were round bottom deep vees with close spaced tiny lifting strakes. That could be what you are thinking of Eric.
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Old 04-20-2013, 02:33 PM   #19
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AusCan, your quite right about drag in smooth water but what your dealing with there is friction. Surprising how much a foot of chop can have on fuel economy at planning speed.
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Old 04-20-2013, 03:26 PM   #20
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Okay, Eric I found a mention of quadruple Jaguar powered Tramontana II racing in 1963 (unsuccessfully) but can find nothing on her design or designer. As I mentioned above the first Tramontana raced in 62 but was outlawed the next year because of excessive HP.

Also in 1965 I found a design by the Scottish firm of G.L. Watson & Co. for a boat called Zingara Mia. She exhibits the same "multi-strake" chine as the original post. The designers call this a "ragged chine" that somewhat produce the effect of a round chine aft without the loss of lift (?) "The chines help to break the slamming." And they go on to claim it's faster than a typical (of the time) deep-vee (???)

I'd say it proved to be a naval architectural dead end.
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