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Old 04-11-2012, 07:18 PM   #101
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Tony B wrote:
" A "displacement hull" is a function of shape. I'm sure I can come up with a box or a barge shape and have a D/L above 260.
The D/L has nothing to do with shape. If I take a Rectangular shape and put a motor on the narrow end, then the length of the water line is measured using the long side of the rectangle.
If on the other hand, I take the same shape and put the motor on the wide end (understandably not the normally desired configuration) then the length of the water line would be the short side of the rectangle
."



.... We are in the Trawler Forum and therefore far from sailing "boxes". All scientists will have different opinions but in this particular case, common sense prevails and we must establish limits for all line of thinking, otherwise we risk to mix apples with oranges, or melons. Yet, I am certain that no matter how much science and theory we put into these floating things, we will never invent in this Forum, another type of hull but the ones already mentioned in the messages above.

As the thread is called “Your hype of hull”, here I go

Mine is a multichine full displacement hull, calculated for 9 knts maximum speed, 7 knots cruising.

Sheers
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Old 04-11-2012, 08:08 PM   #102
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y. The TT,s are, as far as I can recall all semi-disp. Ditto the CHB 34's, the DeFevers, the GB,s and many others. Willard,s and Krogens are Full disp except the Krogen Express.
Our DeFever 48 is really much more of a displacement then a semi-displacement. Might be why it was referred to as a LRC and is much more of a sea boat then many.
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Old 04-11-2012, 08:14 PM   #103
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I was not the one who strayed. I saw what I thought was mis-statement and made a comment.
Anyway, I'm sure glad you cleared that up.
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Old 04-11-2012, 08:26 PM   #104
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Anode,
What on earth kind of engine is a "piggy"?
Eric, maybe he's referring to this little piggy:

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Old 04-11-2012, 09:09 PM   #105
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Eric, maybe he's referring to this little piggy:

Who'd a thunk it? Pigs really do fly. At about 7 knots.
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Old 04-11-2012, 09:29 PM   #106
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how about this one

Rosborough's "inflatable trawler". 30' LOA. 300hp, so I guess they expect it to plane .
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Old 04-11-2012, 09:52 PM   #107
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Ksanders:

If your 4788 has the stock engines, you will never plane. Add 1000 hp and you might. Add 2000 and you will for sure. Don't send me your fuel bill.
The 4788 most definitely planes with 330 b's. 22 knts light and 19 knts heavy. The 4788 planes out at about 14knts. The stern wave pulls away and the wake flattens out. At 26k wet with a very flat hull section it's only compromise is round chines and a partial keel. A full displacement boat cannot plane as the stern will squat deeper and deeper as you add power. There is not enough lift created in the stern sections to begin to skim. Semi displacement boat have flat enough sections in the stern to plane if sufficiently powered. My 48 lrc Hatteras with its 5' draft is a full displacement hull. It has fully round bilges , not chines, with a flatter aft section to keep her from squatting. Double enders have full round bilges and normally no flat sections and squat like mad at anything over hull speed. I guess the bottom line is if you can put enough power to it and it planes its a planing hull.
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Old 04-12-2012, 12:13 AM   #108
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Art,
I've been a bad man. I was much more critical of your post on page 5 than I should have been. Much good and interesting stuff in there. A lot of the Wikipedia stuff was not good or not relative to us. It's interesting how canoes and kayaks can exceed hull speed so well but they can. I have an 18' narrow stern canoe and I've powered it w 6 and 8 hp. Makes about 14 knots. Need weight (wife) to keep the bow down to reasonable attitudes. Without the fwd ballast and w the bow sky high I can do very interesting figure eights. A friend said I was doing canoegies. No I'm not a NA. I've studied it lightly for 55 years. I spent a lot of time in the university branch library in Seattle reading Atkin and other great designers. That was in the mid 50s. My mother was an art teacher and I did lots of drawing.
You're right. One cannot neatly classify many boats like the GB or the DeFevers. The GB is not that far from a planing hull. Take away the big keel, lighten it quite a bit, give it 600hp and off you go planing away without changing the hull shape one bit. The DeFevers act mostly like a full displacement hull most of the time but they have a rather flat QBBL and lots of immersed transom at rest. A flat run aft and a deep flat transom are clearly the features of some kind of planing hull. An underpowered SP or planing hull dos'nt become a displacement hull by adding a big keel and a small engine. I've seen a lot of trawlers in the water that looked like displacement or even FD boats only to see them hauled out to expose their SD or even planing hulls. If I had to make a call on a Camano Troll I'd say it is a planing hull. In the water it looks like it has a deep draft fishing boat hull under but not so. The Camano is a beautiful boat and a good one too from what I hear. I personally can almost always make a call but some seem to be equally two types ......but not many. Anyway I was fiddling around w my i-pad reading posts as in mostly scanning ....and one of those posts was yours.
So I'm glad to hear you're not easily offended.
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Old 04-12-2012, 02:30 AM   #109
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Art,

I've been a bad man. I was much more critical of your post on page 5 than I should have been. Anyway I was fiddling around w my i-pad reading posts as in mostly scanning ....and one of those posts was yours.
So I'm glad to hear you're not easily offended.
Awww Shucks, Eric... don't be too hard on yourself! Anyway, thanks for posting that, and heck, you're way too nice a guy to really offend me. I've got thick skin; you ought to see how heated some biz meetings get. The only people who are never wrong are those who never try. We all make mistakes in understanding others, or in self professed knowledge, or...???

This forum discussion stuff is simply a communicative learning experience for us all; as well as fun and games, at least for me. I do forum time to clear my mind from writing biz documents and working on product plans. Forum offers great relaxation for me while chatting/learning/teaching about boats and other marine items – which I adore! BTW, much of what you post is very interesting and I learn from you, as well as from others. Hope my input also adds a bit of positive influence. I can get a bit opinionated, raspy at times too; I’ve been known to be condescending, as well as occassionally, on the other side, even somewhat thoughtful and understanding. You just never know bout me – that's part of what keeps my nature exciting! Ain’t life grand and boating fun! – Best to ya, and... Cheers, Art
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Old 04-12-2012, 05:54 PM   #110
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ff gave me the idea to see what percentage of hull types are represented on tf. *please participate in the poll so that we can get a good idea.
semi displacement
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Old 04-12-2012, 07:42 PM   #111
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Didn't this originally start as a Poll?
I thought I voted. Did it get erased with all the other changes?
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Old 04-12-2012, 07:51 PM   #112
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Yes it did. I expect the poll itself did not transfer to the new forum format. I haven't looked to see if the new format includes a way to conduct a poll but if there is perhaps Don or whoever put it up in the first place will do so again.
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Old 04-13-2012, 06:48 AM   #113
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"A full time cruising sailboat probably needs new sails after 5 years."

The sails may be shot after 5 years of exposure to the sun.Tho new fabrics are better.

Since 90% of a circumnavigation (2-3 years) is static , in port or anchored that translates to DECADES OF ACTUAL USE.

Assuming the use of a sail cover.

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Old 04-13-2012, 10:52 AM   #114
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I hope that they can retrieve the original data from the poll.
My best guess is that over 90% of the boats on here have semi-displacement hulls.
There has been enough discussion in this post for most people to now know what they have. Even with overlapping designs, the rules are pretty much in place for full displacement and full planing. Everything else inbetween will probably be a semi-displacement.
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Old 04-13-2012, 09:45 PM   #115
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That is what I said on reply #3
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Old 04-14-2012, 06:59 AM   #116
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"the rules are pretty much in place for full displacement and full planing. Everything else in between will probably be a semi-displacement."

IF true that is very sad , because most folks are not willing to pay the SD fuel/noise price to cruise a couple of K faster and sadly have to live with for the SD compromise hull shape 24/7.

At displacement speeds the dragging transom and larger engine /engines cost , perhaps 15 -20% in added fuel burn ,
and the usual flat rear or chines give a poorer displacement speed ride with a snappier roll.

All to do 12 -15 K perhaps 3 times in 30 years?

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Old 04-14-2012, 08:12 AM   #117
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Phil:

Dont ask a guy my age to remember Reply #3 when the the next post is Reply #114
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Old 04-14-2012, 08:49 PM   #118
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Boy Toys

Saw this craft at the marina today. Wonder what his QBBL is? KJ
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Old 04-14-2012, 09:05 PM   #119
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Saw this craft at the marina today. Wonder what his QBBL is? KJ
That is the kind of boat I wanted to buy, but my wife said No, and she bought our ugly slow trawler. maybe in my next life?
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Old 04-14-2012, 10:35 PM   #120
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KJ,
If you understood what the QBBL is then you'd know it would be 0 degrees.
The QBBL stands for Quarter Beam Buttock Line. It is an imaginary line running fore and aft outboard from the keel half way to the chine along the bottom of the aft section of the boat. A steep QBBL will be found on a full displacement boat. A straight QBBL on a full planing boat. Semi-displacement boats will have a QBBL that is moderate. A boats best operational speed will be fortold by the QBBL. By looking at lots of boat buttocks soon you will be able to estimate fairly accurately the operational speed of most any boat, especially slow boats. A boat w a steep QBBL that is also curved (convex) will be even slower. Below is a picture of such a boat.
At the top of page 4 you can see another example of a boat w a steep QBBL. The planing hull you presented is the opposite ........straight.
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