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Old 02-08-2019, 07:26 PM   #201
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I usta work at False Pass in the Nick Bezz days.
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Old 02-08-2019, 07:48 PM   #202
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I usta work at False Pass in the Nick Bezz days.
I fished salmon in southeast back around 1980 seining, I like Alaska and spent years there but I guess New England has too much pull for me to stay in AK. I used to go up to the Grand Banks when US boats still worked there, weather in that region can get brutal. I had the most fun in Ireland but made no money, Gloucester and New Bedford boats fishing on Georges was the best though. Being forced into retirement sucks.
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Old 02-08-2019, 08:16 PM   #203
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With high tech laser measuring equipment:


It should be fairly easy that correct design conditions could fabricate add-on portions for any boat's bottom to alter its shape as desired... i.e. into a different form.


Therefore... D designed hull could become SD designed hull or even a P hull design. The reverse is also possible.

OMG - A whole new boat-product market just opened up.
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Old 02-08-2019, 09:26 PM   #204
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Really...
I would think that would be an obvious no brainer.
I know the Fleming is a highly respected boat but I’m having trouble imagining it in 12’ following seas and matching the Nordhavn for comfort and safety.
Tony has traveled with the 65' Fleming Venture I and II to some interesting far off places. Lots of YouTube videos of his travels to look at. Our own Steve D did the North Atlantic crossing with him.

But, my point was that there are some very well traveled SDs out there. A FD vessel is not the only blue water game in town. A trip offshore in snotty weather in a big sport fishing vessel is quite an eye opener too.
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Old 02-08-2019, 10:56 PM   #205
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Thanks Sunchaser,
Even a planing boat at times can be excellent in big water. So yes FD isn’t required for big water.

But crossing oceans is different. You’re not going out on nice days ... you’re going out on all the days. Basically whatever happens out there you’re going to get. And every boat is different.

Some boats are good at head seas but terrible in following seas. My boat is great at everything but beam seas. Another boats bow interferes w directional stability and another has a stern that causes wandering or worse.
But there are those boats that do excellent (comparitively) at all things. And there’s no perfect boat.

Of the well known SD trawlers (under 50’) what boats are in the near perfect catergory for offshore running, do you think?
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Old 02-09-2019, 05:50 AM   #206
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There's more to seaworthiness of a boat than just hull shape....


More than of a few of all hull shapes and boats less yhan 100 feet have crossed the Atlantic. Some a stunts, and promotions with safety boats...but sso have regular joes in things like production sportfish, etc.


And yes...more possible these days because of better weather forecasting.
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Old 02-09-2019, 08:36 AM   #207
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This is one of the fishing trawlers I used to own, she had 260hp but was designed originally for 100hp. Mine would do 9kts WOT, one with 100hp did 9kts WOT. Of course the hp was to tow a bigger net and mine weighed 50,000 lbs. Attachment 85078
That's what has me scratching my head a bit. Your CD38 (which i really like) has a very similar hull shape to my WC40 from what i can tell in the pic you have shared and the marketing brochure i have on it. Same Royal Lowell designer. Same beam. Different displacement (mine is half). And the CD has an extra foot of draft. But I wonder if your Iroquois had no trawl gear, nothing in the hold etc. and had a 200-300HP engine if she too would easily get up above 10knts like a SD. I dont know if the CD had ballast. Nor if it had an extraordinarily thick hull so i wonder where the weight came from in standard out of the box FD configuration.
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Old 02-09-2019, 10:26 AM   #208
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That's what has me scratching my head a bit. Your CD38 (which i really like) has a very similar hull shape to my WC40 from what i can tell in the pic you have shared and the marketing brochure i have on it. Same Royal Lowell designer. Same beam. Different displacement (mine is half). And the CD has an extra foot of draft. But I wonder if your Iroquois had no trawl gear, nothing in the hold etc. and had a 200-300HP engine if she too would easily get up above 10knts like a SD. I dont know if the CD had ballast. Nor if it had an extraordinarily thick hull so i wonder where the weight came from in standard out of the box FD configuration.
She had concrete ballast, about 3000 lbs. and it had all the gear, winches, net reel, mast, gallows, doors and net. The builders weight without any gear and a 100hp engine was 42,000 lbs. and a designed speed of 8kts., I believe to get 10kts. out of one you'd need to go over Niagara Falls. I should add the disclaimer that I only saw 9kts. once and it was probably fair tide. I usually steamed at 7kts. where it used about 2 gallons an hour in good weather.
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Old 02-09-2019, 11:33 AM   #209
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Of the well known SD trawlers (under 50’) what boats are in the near perfect catergory for offshore running, do you think?
Eric that is a tough question to answer in that the list is very long. PSN mentioned weather awareness. Couple that with a well tended vessel as represented by many on trawler forum and it is well established that go anywhere is the norm. Range of course becomes a limiting factor.

Recently I was in St Lucia. The types of MV that cruise there from Florida is large. Couple that with what we see in Mexico, the PNW, Alaska proper and Europe and it is fair to say most vessels with a SD hull work quite well in smart hands.

Last summer when in Petersburg we spent time with people who routinely cruise from SE Alaska to Seward on their GB 42. Some years ago I chuckled when reading Egret's (N46) posted blog. Several times they met up with a DeFever 44 when in the Southern Chilean waters around the Cape.

Heck, I know of people who bought a DF 49 in the Seattle area and delivered it to England on its own bottom. It really comes down to time, knowledge, vessel soundness and desire. SD vessels have few limitations as compared to FD. And some are faster than their comparable FD cousins. Think bad weather avoidance. An extra few knots is relevant on the open ocean.

Again, read and view Tony Fleming's F65 articles and YouTube presentations. Impressive as is the man. Keep up your good posts and unflinching interest in this subject.
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Old 02-09-2019, 11:57 AM   #210
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When a wave speeds up, physics dictates that it get higher. Go fast enough, and the stern wave is large enough that the stern sinks into a fairly deep hole, eventually going under.
When a wave speeds up it gets longer, not necessarily higher. The height has more to do with the object creating a wave, it's displacement and shape. A planing boat creates a bow wave, the trough is well behind the transom. As a hull without a lot of lift speeds up, the wave it creates is the same length as the planing boat at the same speed but the energy required is much higher, and that energy is spent in building a higher wave.
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The unique thing about a "Full Displacement" hull is that it cannot ever climb over it's bow wave, no matter how much power you apply. This means you can never get up on plane and your speed will be strictly limited by the length of your hull at the waterline.
Never say "never". You can apply a tremendous amount of power to a boat, most normal hull shapes will eventually plane, though some will sink due to lack of freeboard first. Certainly something like a KK would plane. As a practical matter, you would not attempt to do it as the power required would be very large.
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There's more to seaworthiness of a boat than just hull shape....


More than of a few of all hull shapes and boats less yhan 100 feet have crossed the Atlantic. Some a stunts, and promotions with safety boats...but sso have regular joes in things like production sportfish, etc.
The Atlantic has been crossed by kayaks, rowboats, wind surfers, beach cats (numerous times for all of those), inflatable boats, and on at least one occasion each, a floating pile of garbage and a person clinging to a mooring buoy. The smallest boat to do it was just over 5' long. The only challenge for a powerboat is carrying enough fuel.
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Old 02-09-2019, 08:37 PM   #211
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When a wave speeds up it gets longer, not necessarily higher.
So, as a full displacement vessel approaches hull speed, the bow wave speeds up as it lengthens, but you are apparently saying that the bow and stern wave don't also increase in height. Do I understand you correctly? if we can agree that they do increase in height, then you are agreeing with my point, not disagreeing with it.
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Old 02-11-2019, 11:49 AM   #212
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Never, never...

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Never say "never". You can apply a tremendous amount of power to a boat, most normal hull shapes will eventually plane, though some will sink due to lack of freeboard first.
Huh? I was sure we were talking about "FULL DISPLACEMENT" hulls.

Never is the right word. The question is not about '...most normal hull shapes...' (whatever that means). The question is about Full Displacement hulls.


A true 'Full Displacement' hull will never plane out, no matter how much power you put into it, which (if I read you correctly) you seem to acknowledge, like this...

Re: "...though some will sink due to lack of freeboard first."

In the real world of hulls that someone has actually built (or would actually build), a hull that is up on plane cannot 'sink due to lack of freeboard'. If a hull on plane lacks enough freeboard to prevent it sinking, then it would sink immediately as soon as it came down off plane. This would not be called a hull, it would be called an artificial reef.

While we're at it, maybe we need to make sure we're all talking about the same thing when we say 'planing'?

https://www.boatdesign.net/threads/d...planing.45248/

So, when you said that a full displacementy hull 'can be forced to plane, but will sink due to lack of freeboard first' -- how is that different from saying it can never plane?

Re: "You can apply a tremendous amount of power to a boat..."

Tremendous is not enough. How about this. Show the attached photo to any marine architect, and ask them "how much power will I need to get this boat on plane"?
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WP_20171004_12_16_04_Pro.jpg  
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Old 02-11-2019, 12:31 PM   #213
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Actually, I beieve there have been reports of racing sailboats that have gone completely under and popped right back up. They were being driven hard and surfing big swells.


Cant say they were displacement , but they were well betyond hull speed, most likely sleds that develoed too much low pressure below for their shape/bouyancy.
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Old 02-11-2019, 12:35 PM   #214
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Actually, I beieve there have been reports of racing sailboats that have gone completely under and popped right back up. They were being driven hard and surfing big swells.
There's also reports of sailboats being given a tow by ships and being towed under and not popping up.
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Old 02-11-2019, 12:59 PM   #215
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Full Displacement Speed

I find it more helpful to think of full displacement as an operating speed rather than a hull design. A fast boat can run at "full displacement speed." That speed is typically 1.2 x the square root of the waterline (1.34 is the technical number, but not the ideal one).

I worked for a naval architect who was found of saying that if you tied a sailboat (full displacement for sure) to an aircraft carrier, it would plane. As someone said earlier, the accident report would be interesting.

Some boats are designed to operate solely in full displacement mode. Some boats are designed to be semi-displacement, but due to engine choice or poor selection, then can only run in full displacement mode.

As for rolling, I would argue that all boats roll badly at full displacement speeds. Is a hard chine boat any better? Marginally perhaps but they still roll like mad at low speeds in moderate sea conditions.

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Old 02-11-2019, 01:17 PM   #216
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A full displacement trawler is one that displaces it's own weigh to remain afloat and it must push that same weight of water out of it's way to move. Any boat can be over-engined and made to go faster than it's hull speed. Hull speed is the velocity at which power and drag lines cross on a graph, it is where speed and fuel economy are optimized. Planing hulls are typically faster and the "get on plane" meaning they are skimming on top of the water to an extent so that it is not displacing it's weight but rather a combination of buoyancy and the physical action of planing keeps it above water.
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Old 02-11-2019, 01:23 PM   #217
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I can make a square rock plane with my slingshot. Enough power and anything will plane, but likely not in an elegant manner.
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Old 02-11-2019, 01:33 PM   #218
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I find it more helpful to think of full displacement as an operating speed rather than a hull design. A fast boat can run at "full displacement speed." That speed is typically 1.2 x the square root of the waterline (1.34 is the technical number, but not the ideal one).

I worked for a naval architect who was found of saying that if you tied a sailboat (full displacement for sure) to an aircraft carrier, it would plane. As someone said earlier, the accident report would be interesting.

Some boats are designed to operate solely in full displacement mode. Some boats are designed to be semi-displacement, but due to engine choice or poor selection, then can only run in full displacement mode.

As for rolling, I would argue that all boats roll badly at full displacement speeds. Is a hard chine boat any better? Marginally perhaps but they still roll like mad at low speeds in moderate sea conditions.

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"As for rolling, I would argue that all boats roll badly at full displacement speeds. Is a hard chine boat any better? Marginally perhaps but they still roll like mad at low speeds in moderate sea conditions."

You're talking explicitly about beam seas... I take it. And, with a full plane hull, having ample power, there are speed increase levels that can reduce even beam sea rolls. Although adding some time, fuel use and actual boat-through-water/over-land distance... for any shape hull at any speed... angles of tacking through beam sea conditions can help reduce "roll" circumstances.
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Old 02-11-2019, 01:37 PM   #219
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I can make a square rock plane with my slingshot. Enough power and anything will plane, but likely not in an elegant manner.
You can make a rock, or an inner tube, or a canoe plane because it has surfaces that are more or less horizontal to the water, so generates lift to keep it above the water. A full displacement hull has completely inadequate such surfaces and drag will overcome whatever lift the hull does generate, resulting in a swamped boat if pushed. This is an observable phenomenon that has been mentioned by others - FD hulls have been pulled under the water when you overpower them during a tow. According to the theory that any FD hull can plane with enough power is simply incompatible with this observable fact.

Now, if you are talking about strapping a couple of Saturn V rocket engines on each side of a FD boat, then I guess you could turn it into a rocket, Wiley Coyote style. But the idea that a FD boat, under its own power, can power through the bow wave created as you approach hull speed, is simply false.
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Old 02-11-2019, 01:37 PM   #220
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I can't unsee that!
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