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Old 08-04-2013, 07:49 AM   #21
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As a former Professional Captain of excursion vessels, sport fishing charterboat owner/operator, delivery Captain and boat builder/restorer, I know well the frustration felt when one is forced to travel at a no-wake speed. Time is money and yet I have, for the most part, seen that the real working pros do their best to avoid damage to shoreline property whether it be seawalls, docks or boats. Not always possible given the nature,size or operating conditions of their vessel and they are a target for lawsuits.
But a 40' Albin - no excuse! Thats going to be my boat you throw up against the dock and damage, my grandchildren you swamp in their dinghy or my son's seawall you undermine. I'm all for stopping shoreside development but reluctantly respect the rights of those already there.
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Old 08-04-2013, 08:30 AM   #22
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As a former Professional Captain of excursion vessels, sport fishing charterboat owner/operator, delivery Captain and boat builder/restorer, I know well the frustration felt when one is forced to travel at a no-wake speed. Time is money and yet I have, for the most part, seen that the real working pros do their best to avoid damage to shoreline property whether it be seawalls, docks or boats. Not always possible given the nature,size or operating conditions of their vessel and they are a target for lawsuits.
But a 40' Albin - no excuse! Thats going to be my boat you throw up against the dock and damage, my grandchildren you swamp in their dinghy or my son's seawall you undermine. I'm all for stopping shoreside development but reluctantly respect the rights of those already there.
Often I think wake discussins are about 2 different scenarios...

First of all ....after a lifetime on the water...none of my wakes have ever damaged anything or hurt anyone....even by my wake monster which was a 37' sportfish.

There are some real wakes out there doing bad things...but they are not mine.

When I refer to "whiners"...it's the guys who are complaining about a wake size that by late afternoon are dwarfed by the sea breeze against the tide waves.

What got this thread off to the wake tangent was the following picture ...which I can't be totally sure about...but I would hardly worry about that wake unless you were pretty near the docks or vessel you were passing.

My real point is that if you are on the water, sometimes wakes/waves are gonna happen (emergency vessels, nature) , some of the responsibility is yours to be shipshape and seamanlike...one hand for the ship as they say. I hate the expression "you are always responsible for your wake" ....because it suggests to some that as long as they have 1" freeboard on their 12 foot jon boat, it's within there inalienable rights that they can stand up and fish a busy inlet. While legally true...I really have an issue with that mentality whether boating or life in general.
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Old 08-04-2013, 10:08 AM   #23
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dhiggins,

Sounds like you have a semi disp hull if it's like a GB. The formula for HS is 1.34 X the square root of the water line length. Two feet of rake on the stem and the WLL will be 2' less than the overall length.

Semi disp hulls are much less sensitive to hull speed hydrodynamics and tend to respond more like boats called planing hulls. But some semi disp hulls like many DeFevers are quite close to FD hulls and their performance resembles FD hulls more closely. Your boat is probably a tad more like a planing hull than the DeFevers but still may be fairly close to a FD hull.

What this means to you is you can pay less attention to "hull speed" as your boat is more flexible. Like Mark says ... he runs a knot slower than HS. Actually that's the only reasonable option he has. Running HS on a FD hull is making a big wake and as Mark says burning TWICE as much fuel. Sure he can but most all knowledgable FD skippers will run one knot below HS.

Semi Displacement hulls can, rather gracefully, run one knot OVER hull speed as well as exactly at hull speed. They are designed to do so. The GBs are an excellent example. A 36 GB w 250hp will run 8 or 9 knots all the time. That's the glory of the SD hull. It goes faster and does it gracefully. Actually I'm quite sure a FD hull will burn more fuel at hull speed that a SD. Burning considerably more fuel and going more than HS is so desirable (since fuel is cheap) most all trawlers are SD as I think your's is.

It sounds like you've got a GB or a boat like a GB w a single engine. If you want (looks like it) to go over 7 knots there are lots of twin engined boat owners that are fixated on low fuel consumption that will probably trade for your more economical boat. Or do a good job of selling yours and buy a twin that will probably be cheaper. Most trawler owners and shoppers think single engined boats are better. You can use this to your advantage.

Edit:
Just read your OP. We need to know what kind of hull you have but if it's like a old GB yes you can put a bigger engine and go 8 knots or even 9 or 10 if you are willing to pay the fuel burn. If you have an Island Gypsy it may go faster than a GB. What have you got?
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Old 08-04-2013, 11:18 AM   #24
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Don't want to hear any complaints about this 5-plus-knot wake!:



Further up the river/slough it is narrower; we got "dirty" looks from a couple of on-shore fishermen. They didn't seem concerned with our itty-bitty wake, but they had their lines out in the middle of the channel, and we were apparently disturbing them.
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Old 08-04-2013, 12:00 PM   #25
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...
To prove my point...if you run the ICW...you'll see almost all new properties along the way have boat lifts and there aren't ANY state placed no wake buoys.
If one is wealthy enough, you can afford both a boat lift and a personal "no wake" sign (as well as a very large house with comparable swimming pool and acreage), leastwise along the Petaluma River:

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Old 08-04-2013, 12:22 PM   #26
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In California: "The maximum speed for motorboats within 100 feet of a bather (but not a water skier) and within 200 feet of a bathing beach, swimming float, diving plaform, or life line, passenger landing being used, or landing where boats are tied up is five miles and hour." (emphasis added) Who said anything about a no-wake zone?
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Old 08-04-2013, 01:55 PM   #27
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In California: "The maximum speed for motorboats within 100 feet of a bather (but not a water skier) and within 200 feet of a bathing beach, swimming float, diving plaform, or life line, passenger landing being used, or landing where boats are tied up is five miles and hour." (emphasis added) Who said anything about a no-wake zone?
Which makes sense...but only to my point...5 mph is which?

5 mph through the water or over ground? If 5 through the water...then if a 4-5 knot current...commerce all but stops or backs up...5 mph over ground is 10 mph through the water and results in a huge wake...

Wake laws are written poorly, adhered to poorly and supported without the big picture in mind much of the time.
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Old 08-05-2013, 12:54 PM   #28
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Is appears some of you guys are on the wrong post. This was a question/info post on hull speed/engine HP, not wakes and law enforcement. Thanks.
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Old 08-05-2013, 01:00 PM   #29
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I'm sad to say my boat has a full displ. hull. So I guess I'm stuck with the 8 kt. hull speed.
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Old 08-05-2013, 04:22 PM   #30
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Psneedl. Some people like to run off half cocked before knowing the whole story.

Everyone needs an education now and then.

In this regard you are spot on.

SD
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Old 08-05-2013, 04:42 PM   #31
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I'm sad to say my boat has a full displ. hull. So I guess I'm stuck with the 8 kt. hull speed.
Yes. You have the wrong boat ... unless you're in a no-wake zone.

If it helps: I find if I look down at the water, it seems the boat is going faster than it is.
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Old 08-08-2013, 06:43 AM   #32
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HULL Speed is great mental masturbation but mostly useless for most marine motorists.

CO$T is the simple answer , boats that will burn minor fuel at 6K may double the burn going 7K and double it again attempting 8K.

For almost all displacement boats where the beam is about 1/3 the length , the square root of the LWL (underway) is the cheapest speed.

For a cheap 8K cruise a 64 ft LWL would be required.

Sailors may actually see or better hull speed IF its blowing hard enough,
tho most sail cruisers shorten sail for a better ride in 30K breezes.
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Old 08-08-2013, 10:14 AM   #33
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dhiggins,
We can't make any really definitive response to your original post w/o seeing or knowing how you're boat is shaped below the WL especially aft. Most people don't really know the difference between a FD and SD hull and you (until we see otherwise) are probably "most people".

However if you were to say your transom is entirely out of the water we would know you have a FD hull. Even if it was double ended ... there are planing double enders so that wouldn't be conclusive.

Also if your boat can go more than one or 2 knots over hull speed it id SD. FD boats are not capable of that at all. I have a FD boat that requires doubling it's power to gain one knot over HS and I don't think doubling it again would gain another knot. To my knowledge it has never been done either.

Can you post a picture of your boat? There are instructions here on the forum on how to do that. Look at the top where it says "Forum Support"..... . I had to learn. When I started here I didn't know.

If your boat looks very much like either of these two boats in the stern it's probably FD. Ignore the keels. The rest of the boat (red bottom) is the definitive part. If it has a rather flat transom w about 6" or more submerged below the WL at rest it's probably not a FD boat. If the stern of your boat looks somewhat like the bow it is very likely a FD hull.

Your picture will tell if it's of the stern ... preferably out of the water.
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Old 08-11-2013, 03:49 AM   #34
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dhiggins,

Sounds like you have a semi disp hull if it's like a GB. The formula for HS is 1.34 X the square root of the water line length. Two feet of rake on the stem and the WLL will be 2' less than the overall length.

Semi disp hulls are much less sensitive to hull speed hydrodynamics and tend to respond more like boats called planing hulls. But some semi disp hulls like many DeFevers are quite close to FD hulls and their performance resembles FD hulls more closely. Your boat is probably a tad more like a planing hull than the DeFevers but still may be fairly close to a FD hull.

What this means to you is you can pay less attention to "hull speed" as your boat is more flexible. Like Mark says ... he runs a knot slower than HS. Actually that's the only reasonable option he has. Running HS on a FD hull is making a big wake and as Mark says burning TWICE as much fuel. Sure he can but most all knowledgable FD skippers will run one knot below HS.

Semi Displacement hulls can, rather gracefully, run one knot OVER hull speed as well as exactly at hull speed. They are designed to do so. The GBs are an excellent example. A 36 GB w 250hp will run 8 or 9 knots all the time. That's the glory of the SD hull. It goes faster and does it gracefully. Actually I'm quite sure a FD hull will burn more fuel at hull speed that a SD. Burning considerably more fuel and going more than HS is so desirable (since fuel is cheap) most all trawlers are SD as I think your's is.

It sounds like you've got a GB or a boat like a GB w a single engine. If you want (looks like it) to go over 7 knots there are lots of twin engined boat owners that are fixated on low fuel consumption that will probably trade for your more economical boat. Or do a good job of selling yours and buy a twin that will probably be cheaper. Most trawler owners and shoppers think single engined boats are better. You can use this to your advantage.

Edit:
Just read your OP. We need to know what kind of hull you have but if it's like a old GB yes you can put a bigger engine and go 8 knots or even 9 or 10 if you are willing to pay the fuel burn. If you have an Island Gypsy it may go faster than a GB. What have you got?
Hi Eric,
You seem to have a very considerable interest in this subject of hull speed.
I thought you might enjoy looking at this initial posting by a gentleman Mike D who was very well regarded, but has since passed away a number of years ago:
Hull speed - Boat Design Forums

Quote:
Notes on hull speed and the gross misconceptions surrounding it. These notes concern displacement craft.
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Old 08-11-2013, 10:28 AM   #35
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Semi Displacement hulls can, rather gracefully, run one knot OVER hull speed as well as exactly at hull speed.
Not being a NA or a desire to be one, I have observed over the years that the above statement is true! At least my boat acts like that. It will go faster, however, with a different propeller or larger engine. I was told by Harvey Halvorsen a few years ago that they put a large engine in a 32' Island Gypsy and got her up to 20+ knots.
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Old 08-11-2013, 10:37 AM   #36
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Walt re your boat going 20 knots ... yes she can.

Brian I think I've seen that but will study that or/and review. Yes I've always been fascinated w hull form and the dynamics. Thanks
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Old 08-11-2013, 12:41 PM   #37
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Brian,
Very good indeed.especially the part about the nose getting ahead of the chin.

When I get home I'll bookmark that one to study. I don't understand enough about fourd's law. It's talked about a lot on BDesign so I need to understand it. Thanks for the link.

Brian I'm Easy Rider on BD. Would like to know your username there. PM

I have a thing called "effective hull speed" that I made up. I feel the effects of hull speed on hulls very full at the ends probably are different from hulls that are very "pointy" at the ends. A FD hull very full at the ends like some Dutch craft should have the ability to go faster (although needing more power) because the "effective" WLL is greater even though the physical WLL is the same.

Anybody see my point and have an opinion?
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Old 08-11-2013, 01:28 PM   #38
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Brian,
Very good indeed.especially the part about the nose getting ahead of the chin.

When I get home I'll bookmark that one to study. I don't understand enough about fourd's law. It's talked about a lot on BDesign so I need to understand it. Thanks for the link.

Brian I'm Easy Rider on BD. Would like to know your username there. PM

I have a thing called "effective hull speed" that I made up. I feel the effects of hull speed on hulls very full at the ends probably are different from hulls that are very "pointy" at the ends. A FD hull very full at the ends like some Dutch craft should have the ability to go faster (although needing more power) because the "effective" WLL is greater even though the physical WLL is the same.

Anybody see my point and have an opinion?
Pretty sure that's Prismatic Coefficient....

here's one view of it...

"The prismatic coefficient (P.C.) is a technical term used to define how displacement is distributed along a hull, or how fine or full the ends of the hull are......"

Prismatic Coefficient - Fontaine Design Group-Super yacht Designer

like what Sceptic said....
"There is a poster here who thinks the performance of a boat is based almost entirely on the stern. He never shows any evidence that he knows anything about block, or prismatic coefficients."
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