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Old 09-18-2010, 09:27 PM   #41
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RE: First post, and yet another "what boat" post

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syf350 wrote:I thought trawlers were full displacement?
Well, real trawlers, the ones that pull a trawl net around, are invariably full displacement just like most commercial fishing boats.

The term "trawler" as applied to the kinds of boats we talk about on this forum is nothing but marketing hype, a name glommed onto because of the image of a tough, stable, go-anywhere fishing boat.* So with regards to our boats, it's a totally meaningless term.* They could have as easily called them Nogginhulls--- the name would have been as accurate.

The upside of a displacement hull (there's no such thing as a "full-displacement" hull-- that's what the term "displacement" means--- it either is or it isnn't) is that it's very seaworthy and very exononmical to drive though the water.* Since it can't go any faster than it's displacement speed, once you have enough power to achieve that, adding more does nothing other than dig a deeper hole in the water.

Hence the "semi-planing" hull which a lot of people and manufacturers insist on calling a semi-displacement hull even though that's an inaccurate term.** As John said, a semi-planing hull buys you a greater degree of stability--- which is not the same thing as a greater degree of seaworthiness--- and it can be driven at faster-than-displacement speed because of the flatter aft secton of the boat lifts the hull up to a degree which reduces drag and allows the hull to move faster through the water.

Anything that when out of the water has a hull bottom that looks like a Grand Banks, CHB, etc., etc., etc. is a semi-planing boat.* So despite the meaningless term, it's safe to say that most---not all--- recreational "trawlers" are semi-planing.

Wet ride.* Our Grand Banks has a very wet ride even at 8 knots (or less).** This is because there is very little flare in the cross-section of the forebody of the hull.* So when heading into, or quartering into, waves, particuarly on a windy day which up here is most of them, the waves whack into the hull and go ripping up the sides.* But instead of this rising water being thrown out and down, on a GB it goes straight up higher than the gunwale where the wind then catches it and slams it into the boat's superstructure, mainily the front and forward sides of the cabin.* On our GB on a typical Bellingham Bay day, our windshield wipers, which fortunately do an excellent job, are going most of the five mile run across the bay even on a "nice" day.* That's a wet ride.

A boat with a lot of flare in the bow, or with spray rails down near the waterline, won't throw as much water vertically into the air where the wind can catch it and blow it onto the boat.* That's a "dry ride."

Wet and dry rides often have nothing to do with speed.* It's all about hull shape.* There were two main types of PT boats used in WWII.* One was made by Elco, the other by Higgins.* While they were designed to the same mission specs they were signficantly different int their hull configurations.* The 78' Higgins boat, while faster and (some said) a bit more maneuverable had an extremly wet ride (which made for a wet crew).* The 80' Elco boat had more flare and width in the forebody and had a dry ride even at its maximum speed of some 45 mph.

*
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Old 09-19-2010, 06:28 AM   #42
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RE: First post, and yet another "what boat" post

John and Marin, thanks for the info. I've learned a lot. Hope Josh has too.
I received this advice several months ago: Also, that boat really improves its rough water performance if you install spray rails forward, either glue on or screw on.* Not too much bow flair with Carvers.* The rails virtually eliminate the water spray from off center wave action, throwing it away from the boat- also can punch through much easier.
I'm really not sure what's involved to accomplish this, but this advice came from a very knowledgeable Carver owner. I have noticed even in calm water at 20 kts, spay will reach the bridge.

Anybody know what's involved with adding spay rails?
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Old 09-19-2010, 08:04 AM   #43
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First post, and yet another "what boat" post

Interesting topic & an answer to your question about adding spray rails.

Older Island Gypsies had no spray rails and not much bow flair, so water tended to climb the hull, and with any wind at all, you had a wet boat. With the addition of spray rails, this condition improved but did not totally eliminate the problem.

My own boat has Smart Rails and is running at 8 knots in the photo below.
Here's a good source if you want to educate yourself about spray rails. (Smart Rails?)
Smart rails


-- Edited by SeaHorse II on Sunday 19th of September 2010 08:15:05 AM
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Old 09-19-2010, 08:31 AM   #44
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First post, and yet another "what boat" post

Tim, the spray rails may improve the wetness or dryness of your ride, but it will do nothing for the dynamic action of your boat moving thru the water. Your quote made it sound like somehow, the rails would make the boat "punch thru" the waves much easier. I don't see how.

-- Edited by Baker on Sunday 19th of September 2010 08:32:11 AM
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Old 09-19-2010, 08:52 AM   #45
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RE: First post, and yet another "what boat" post

First off, yes, I am learning a great deal and especially appreciate the time yall have spent in the replies.

Another question and surely to be a dumb one (there really are such things!)

Can taking a carver or bayliner type planning hull and just slowing it down to displacement speeds make it any more "seaworhty"?
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Old 09-19-2010, 10:09 AM   #46
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RE: First post, and yet another "what boat" post

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syf350 wrote:

First off, yes, I am learning a great deal and especially appreciate the time yall have spent in the replies.

Another question and surely to be a dumb one (there really are such things!)

Can taking a carver or bayliner type planning hull and just slowing it down to displacement speeds make it any more "seaworhty"?
The short answer is NO! *The boat is what it is. *Your question entails the judgement of the operator/captain. *To put it another way, the way the captain operates the boat will have an effect as to the outcome of the journey. *So if conditions warrant slowing down, then so be it. *Slowing down will have an effect on fuel consumption.

Also to reference hullshape and why slow planing hull does not equal displacement hull at same speed........ * * * * * *A planing hull has a lot of flotation along the full length of the hull will sit "on top" of the water whereas a displacement hull will be submerged in it. *Small wave action has the ability to upset a boat on top of the water because it can get "underneath" the floating section on the hull. *A full displacement hull does not suffer this because the hull is fully submerged and is one with the body of water it is in. *Surface action may cause it to gently sway but it won't upset. *To put it another way, a planing hull is part of the surface of the water and is upset by things on the surface. *A full displacement is more deeply rooted in the body of water and not as easily upset by surface action.


Please realize I have absolutely no training in all of this but just kinda thinking out loud....with common sense....and ignorance!!!!...


If you get a planing hull(semi or otherwise) up on plane, it then becomes more stable due to the dynamic pressure on the hull(lift). *And like Marin said somewhere, stability does not necessarily mean seaworthy.




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Old 09-19-2010, 10:22 AM   #47
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RE: First post, and yet another "what boat" post

Let's add some practicality to all of this. Most of the boats on here are semi-planing hulls. If you asked their owners...."You are in the weather and it is fairly rough/choppy....what part of the hull would be the most comfortable to take that weather???"????? And they would all answer "on the nose"!!!

Why???

Because the bow of the boat is the "displacement" part of the boat. It has very little flotation up there and it is pretty much full submerged. A wave comes and it goes THROUGH it and not OVER it.

Now ask them the worst "point of sail"....and that would be to take the weather on the stern.

Why?

For the opposite reason. All of these boats have big square floaty asses. You put a wave up underneath them and they float up with the wave(and cause steering issues but that is another discussion). This is not comfortable and requires a lot of work on the part of the helmsman....human or otherwise. And could be dangerous as the conditions become more extreme.

A true full displacement boat would simply float up with the wave but would track straight since the dynamic pressure on the hull would be relatively equal. If you have had a sailboat in following seas you realize that it is not that big of a deal. It is a PIA in a semi boat!!!!
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Old 09-19-2010, 11:09 AM   #48
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RE: First post, and yet another "what boat" post

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Baker wrote:

Tim, the spray rails may improve the wetness or dryness of your ride, but it will do nothing for the dynamic action of your boat moving thru the water. Your quote made it sound like somehow, the rails would make the boat "punch thru" the waves much easier. I don't see how.

-- Edited by Baker on Sunday 19th of September 2010 08:32:11 AM
John, I'll try and found out what he meant by that.

*
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Old 09-19-2010, 12:16 PM   #49
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RE: First post, and yet another "what boat" post

All a spray rail does is help prevent water/waves that are hitting the hull (or are being hit by the hull) from climbing the side of the boat and being blown on board by the wind. They don't do anything noteworthy with regards to the handling or seaworthiness of the boat. For example, all newer GBs with over x-amount of horsepower have spray rails. This is because these boats can be driven fast enough to really bash up a bunch of water, so the rails help cut the amount of water that comes on board. But the handling and seaworthiness of these boats is no different than comparable models with lower horsepower and no spray rails.
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Old 09-20-2010, 04:12 AM   #50
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RE: First post, and yet another "what boat" post

looking to start off easy, some ICW, perhaps more of the great loop, ultimately Caribbean, bahamas, and who knows after that if the lifestyle is for us.


What you have described as your cruising area would not require an ocean worthy boat,(@$300% higher cost) most anything you can fit on and afford to buy fuel for will be just fine.Even a Bayliner.

The first contemplation is traveling fuel costs, gas or diesel .

Most Great lakes folks go for Gas as its used in plaining boats , for rapid runs between marinas.

Diesel will do better in displacement boats , far slower but 2 or 3 NMPG , eg 7K at 3 gph is fairly common. The gas boat may require 30gph to run 15K , so on;ly .5 NMPG

Try plaining a diesel, as the fish killers do, and the fuel burn is also high .

The maint expenses are far lower with Gas , so if you will be dockside the wear
out of 2000 hours vs 5000 -7000 hours for diesel will be no problem.

The cash saved cam pay for lots of fuel.
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