Reply
 
Thread Tools Display Modes
 
Old 02-24-2012, 07:03 AM   #1
Guru
 
Moonstruck's Avatar
 
City: Hailing Port: Charleston, SC
Country: USA
Vessel Name: Moonstruck
Vessel Model: Sabre 42 Hardtop Express
Join Date: Nov 2008
Posts: 7,848
Your hull type

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.
__________________
Advertisement

Moonstruck is offline   Reply With Quote
Old 02-24-2012, 08:45 AM   #2
Senior Member
 
bshanafelt's Avatar
 
City: Seattle, WA
Vessel Name: Isobel K
Vessel Model: 37' Custom Pilothouse
Join Date: Oct 2007
Posts: 288
RE: Your hull type

full
__________________

bshanafelt is offline   Reply With Quote
Old 02-24-2012, 08:52 AM   #3
Guru
 
Phil Fill's Avatar
 
City: Everett Wa
Country: US
Vessel Name: Eagle
Vessel Model: Roughwater 58 pilot house
Join Date: Oct 2007
Posts: 2,919
RE: Your hull type

I question the % of full displacment as most pleasure trawler as semi displacemnt.* The*popular*TRUE full displacment are Nordhavn, Krogan, and Selene.*As far as I am concern 90% of the pleasure trawler as semi displacement.*

So maybe a definition of full and semi displacment is needed first.*

*

*
Phil Fill is offline   Reply With Quote
Old 02-24-2012, 09:15 AM   #4
Guru
 
Moonstruck's Avatar
 
City: Hailing Port: Charleston, SC
Country: USA
Vessel Name: Moonstruck
Vessel Model: Sabre 42 Hardtop Express
Join Date: Nov 2008
Posts: 7,848
RE: Your hull Whtype

Quote:
Phil Fill wrote:
I question the % of full displacment as most pleasure trawler as semi displacemnt.* The*popular*TRUE full displacment are Nordhavn, Krogan, and Selene.*As far as I am concern 90% of the pleasure trawler as semi displacement.*

So maybe a definition of full and semi displacment is needed first.*

*

Phil, I think you are mostly right, but maybe Willards and a few others could be added. *Maybe the question should have been what kind of hull do you think you have. *We also have no way of knowing if someone with a semi displacement hull running at displacement speeds has checked full displacement. *Where is Eric when we need him? **
*
Moonstruck is offline   Reply With Quote
Old 02-24-2012, 09:40 AM   #5
Guru
 
psneeld's Avatar
 
City: Avalon, NJ
Country: USA
Vessel Name: Freedom
Vessel Model: Albin 40
Join Date: Oct 2011
Posts: 15,902
Your hull type

Quote:
Moonstruck wrote:Phil Fill wrote:
I question the % of full displacment as most pleasure trawler as semi displacemnt.* The*popular*TRUE full displacment are Nordhavn, Krogan, and Selene.*As far as I am concern 90% of the pleasure trawler as semi displacement.*

So maybe a definition of full and semi displacment is needed first.*

*

Phil, I think you are mostly right, but maybe Willards and a few others could be added. *Maybe the question should have been what kind of hull do you think you have. *We also have no way of knowing if someone with a semi displacement hull running at displacement speeds has checked full displacement. *Where is Eric when we need him? **
*

*While I at first agreed with this logic...I woke up and realized it's just going to be one huge discussion that can't be resolved unless someone wants to be very*specific which rarely occurs in these forums.

While most of the 1970s-1990s "typical" trawler designs I would agree more closely resemble semi-displacement...they are so poorly designed to be semi-displacement that pushing them even 1 knot over hull speed results in a drastic increase in fuel consumption and stern wave.

That by definition is sorta like full displacement even though they aren't full displacement based on energy required to drive them at hull speed...what the heck????

So how do I answer?????* *


-- Edited by psneeld on Friday 24th of February 2012 10:41:41 AM
psneeld is offline   Reply With Quote
Old 02-24-2012, 10:06 AM   #6
Guru
 
Join Date: Aug 2011
Posts: 511
RE: Your hull type

I've got a "semi" LOL
twiisted71 is offline   Reply With Quote
Old 02-24-2012, 10:53 AM   #7
Master and Commander
 
markpierce's Avatar
 
City: Vallejo CA
Country: USA
Vessel Name: Carquinez Coot
Vessel Model: 2011 Seahorse Marine Coot hull #6
Join Date: Sep 2010
Posts: 10,262
Your hull type

Believe the Coot has a semi-displacement/planing*hull.* But since she has insufficient horsepower to plane and moves through rather than on the water, it qualifies as a "trawler" rather than "sedan cruiser" using Chapman's definitions.

Perhaps it would be helpful if the ratio*of theoretical hull speed versus maximum speed is calculated

For the Coot: 1.34 times the square root of 31.75' waterline equals theoretical max. hull speed of 7.55 knots.* Actual maximum speed is 7.7 knots, giving*a ratio of 1.02.


-- Edited by markpierce on Friday 24th of February 2012 12:09:56 PM
Attached Thumbnails
Click image for larger version

Name:	hoisted2.jpg
Views:	116
Size:	174.1 KB
ID:	10283   Click image for larger version

Name:	hoisted.jpg
Views:	115
Size:	94.4 KB
ID:	10284   Click image for larger version

Name:	exhaust.jpg
Views:	116
Size:	56.2 KB
ID:	10285  
markpierce is offline   Reply With Quote
Old 02-24-2012, 10:59 AM   #8
Guru
 
Woodsong's Avatar
 
City: Atlanta
Country: USA
Vessel Model: Bayliner 4550 Pilothouse
Join Date: Oct 2007
Posts: 1,630
RE: Your hull type

Which boat?? I have one semi-displacement, one planing.
Woodsong is offline   Reply With Quote
Old 02-24-2012, 11:07 AM   #9
Guru
 
Moonstruck's Avatar
 
City: Hailing Port: Charleston, SC
Country: USA
Vessel Name: Moonstruck
Vessel Model: Sabre 42 Hardtop Express
Join Date: Nov 2008
Posts: 7,848
Your hull type

Quote:
Woodsong wrote:
Which boat?? I have one semi-displacement, one planing.
*How about the one you're keeping. *Under that logic I have several homes.

For anyone who has doubts about which form your hull is, wait until Eric (Nomadilly) checks in. *He can tell you.


-- Edited by Moonstruck on Friday 24th of February 2012 12:13:15 PM
Moonstruck is offline   Reply With Quote
Old 02-24-2012, 11:40 AM   #10
Guru
 
Tony B's Avatar
 
City: Joe Wheeler State Park, Al
Country: Cruising/Live-Aboard USA
Vessel Name: Serenity
Vessel Model: Mainship 36 Dual Cabin -1986
Join Date: Jul 2011
Posts: 1,250
Your hull type

I really should not have voted because it taints the desired rusults of a study because I currently iwn a sailboat.

I dont remember the exact requirements to be considered full or semi-displacement but there is a significant difference in design. The one thing I am almost positive about is that with a full displacement hull, you can never plane. The boat would tend to porpose at a particular speed but not plane. I am not sure but I think a semi-displacement hull is similar to full displacement in the front but tends to flatten out some toward the rear.

If you look at a typical full displacement sailboat hull in the water (in the boat slip) down at the rear at the waterline, the boat comes to a point with no flat stern area in the water. It is designed so that while moving, the bow pushes the water aside and then this water moves along the sides of the hull and smoothly comes back to the pointed (rounded)*area and actulaay helps push the boat forward. A flat stern in the water creates turbulance at the stern which requires more power to propel it.

*

*

*


-- Edited by Tony B on Friday 24th of February 2012 12:47:00 PM
Tony B is offline   Reply With Quote
Old 02-24-2012, 01:08 PM   #11
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,525
RE: Your hull type

Simply look at the stern.

The width of the transom at the WL in feet will be close to the speed expected in K.on a 40-50 ft boat.
FF is offline   Reply With Quote
Old 02-24-2012, 01:42 PM   #12
Guru
 
City: Hotel, CA
Country: Fried
Join Date: Sep 2011
Posts: 8,328
RE: Your hull type

If that where the case FF, Don wouldn't be talking about passing the boats that are cruising in front of him at 24 knots
CPseudonym is offline   Reply With Quote
Old 02-24-2012, 01:53 PM   #13
Guru
 
Moonstruck's Avatar
 
City: Hailing Port: Charleston, SC
Country: USA
Vessel Name: Moonstruck
Vessel Model: Sabre 42 Hardtop Express
Join Date: Nov 2008
Posts: 7,848
RE: Your hull type

Quote:
CPseudonym wrote:
If that where the case FF, Don wouldn't be talking about passing the boats that are cruising in front of him at 24 knots
*That's probably a pretty good rule of thumb for most boats. *Once the transom breaks free and is above the surface, the speed is limited by the power and stability of the hull. *In my case 1000 hp and gobs of torque will take it well over the hump. *When the weather is good, we run offshore as much as possible. *In the waterway, we sometimes have to slow pass 25-35 boats. *That gets tiring, but that's how it is. *We don't mind anyone out there sail or trawler. *It's theirs too. *

Sometimes we are one of the few fast cruisers out with the trawlers. *The only real difference in our cruising style is speed. *Oh yeah, we burn a litt.le more. *That is the trade off. *Not being fully retired, we don't have the time some do. *We are willing to make that trade off.
Moonstruck is offline   Reply With Quote
Old 02-24-2012, 02:25 PM   #14
Scraping Paint
 
City: -
Country: -
Join Date: Oct 2007
Posts: 13,748
Your hull type

Quote:
markpierce wrote:
Believe the Coot has a semi-displacement/planing*hull.
*From your photos I would agree although the bottom of your boat has more curved sections than the typical semi-planing hull used on something like a GB, CHB, etc.

To me a displacement hull is one that, while it can be forced a bit faster through the water with the application of a huge amount of power, most of that engergy is absorbed by the hull digging a deeper hole in the water.

A semi-planing hull (I agree with naval architects like Tom Fexas that semi-displacement is simply a marketing term) is one in which an addition of a lot of power results not in the boat digging a deeper hole but in generating enough hydrodynamic pressure against the flatter surfaces of the hull to begin to lift it up in the water, thus reducing wetted surface, thus reducing drag, thus enabling it to go faster albeit with an increase in fuel burn--- very possibly a significant increase as in the case of the previous generation of GB hulls.

A planing hull is just that.* A hull that is designed to generate the maximum possible hydrodynamic force against the wetted surfaces of the hull and thus lift the hull a lot and reduce the drag a lot in as efficient a manner as possible.* This in turn means the boat can go considerably faster than a semi-planing boat with the same power and WAY faster than a displacement boat of the same length, and the greater speed makes the increased fuel burn at least theoretically a good return on the investment.

Those are my definitions of the three hull types.* So based on them, I would say Coot has a semi-planing hull but a pretty inefficient one if one actually wanted to take advantage of its ability to be lifted and reduce the wetted surface and drag.* Major power would be needed.*

So why use a semi-planing hull on a low-powered boat like the Coot or an early GB?** One advantage of this hull type even at slow speeds is that the flat after-section, sharp-chined hull will provide a less rolly ride than a hull with a typical, rounded displacement configuration.* This is certainly true of our GB.* However, less roll comes with a price in that the characteristics of the roll with its sharper "snap back" are uncomfortable to a lot of people.

The second advantage is that a semi-planing hull can be driven a little bit faster than displacement speed with the application of not-that-much-more power.* So while the displacement speed of our hull is seven-point-something knots, the hull can be driven at eight, eight and a half knots without a lot more power or fuel burn needed.* A half to a whole knot more speed doesn't sound like much but to a lot of people--- and the sales department--- it is.

The hull on our boat could be driven at 14 knots or so.* Later GB36s with big engines can achieve this.* But at that point the fuel burn becomes enormous.


-- Edited by Marin on Friday 24th of February 2012 03:28:03 PM
Marin is offline   Reply With Quote
Old 02-24-2012, 02:28 PM   #15
Guru
 
City: Hotel, CA
Country: Fried
Join Date: Sep 2011
Posts: 8,328
RE: Your hull type

Quote:
Moonstruck wrote:The only real difference in our cruising style is speed. *Oh yeah, we burn a litt.le more. *That is the trade off. *Not being fully retired, we don't have the time some do. *We are willing to make that trade off.
*That's the direction the wife and I are leaning. I have a ways to go before slowing down and retiring. We are willing to make the trade off as well. Our first power boat will most likely be a 30ish foot with 20+ knot speed as well... We are enjoying the sailboat in the meantime.
CPseudonym is offline   Reply With Quote
Old 02-24-2012, 02:30 PM   #16
Guru
 
Woodsong's Avatar
 
City: Atlanta
Country: USA
Vessel Model: Bayliner 4550 Pilothouse
Join Date: Oct 2007
Posts: 1,630
RE: Your hull type

Quote:
Moonstruck wrote:Under that logic I have several homes.
*



-- Edited by Moonstruck on Friday 24th of February 2012 12:13:15 PM

*
We can't all by high rollers like you Don!! *

Actually...I assume our 45 is a planing hull. *She has a small keel, prop pockets, and soft chines. *When I haul her out I will take pics.
Woodsong is offline   Reply With Quote
Old 02-24-2012, 02:52 PM   #17
Guru
 
Moonstruck's Avatar
 
City: Hailing Port: Charleston, SC
Country: USA
Vessel Name: Moonstruck
Vessel Model: Sabre 42 Hardtop Express
Join Date: Nov 2008
Posts: 7,848
RE: Your hull type

Quote:
Woodsong wrote:Moonstruck wrote:Under that logic I have several homes.
*

*
We can't all by high rollers like you Don!! *

*

*Yes, you can be a high roller too. *Several are for sale. *You can be a real estate mogul in no time.
Moonstruck is offline   Reply With Quote
Old 02-24-2012, 09:02 PM   #18
Guru
 
koliver's Avatar
 
City: Saltspring Island
Country: BC, canada
Vessel Name: Retreat
Vessel Model: C&L 44
Join Date: Nov 2007
Posts: 2,169
RE: Your hull type

The ultimate semi-planing hull is the Canadian Navy Frigate, Halifax Class. It pokes along under diesel power, to 16 knots, displacement speed. When the gas turbine engine is used, it planes at 40 knots.
koliver is offline   Reply With Quote
Old 02-24-2012, 10:05 PM   #19
Master and Commander
 
markpierce's Avatar
 
City: Vallejo CA
Country: USA
Vessel Name: Carquinez Coot
Vessel Model: 2011 Seahorse Marine Coot hull #6
Join Date: Sep 2010
Posts: 10,262
RE: Your hull type

I thought it was 29 knots.

markpierce is offline   Reply With Quote
Old 02-24-2012, 10:47 PM   #20
TF Site Team
 
ksanders's Avatar
 
City: SEWARD ALASKA
Country: USA
Vessel Name: LISAS WAY
Vessel Model: BAYLINER 4788
Join Date: Feb 2011
Posts: 3,954
Your hull type

Quote:
Woodsong wrote:
Actually...I assume our 45 is a planing hull. *She has a small keel, prop pockets, and soft chines. *When I haul her out I will take pics.
Actually I'd venture to say that you have a semi displacement hull. Thats what I think of our 4788 as.

As you indicated she has a full keel, and soft chines.

I've found that mine even at 15 knots is not realy "over the hump" like our planing hull cruisers were.

I could be wrong, but that seems to fit the definition of "semi displacement" *that boat builders and the public have come to use to define a boat that exceeds hull speed but is not as fast as a "cruiser".

That said, I tend to agree with Beebes definition of boat hulls* being either displacement or planing. Using Voyaging Under Power as a guide we own planing hull boats.

Perhaps a better poll would be " What is the maximum speed of your boat"

The link below is to Bruce Roberts site and is his opinion of the differences between hull forms.

http://www.bruceroberts.com/public/H...OAT_DESIGN.htm*


-- Edited by ksanders on Saturday 25th of February 2012 09:20:06 AM
__________________

ksanders is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Type of caulking and bedding material rusbet General Maintenance 31 04-13-2016 07:15 AM
Dinghy - What type? Tony B Dinghys and Smaller Boats 77 02-27-2014 01:57 AM
Which type of circuit breaker? Shoalwaters Electrical and Electronics & Navigation 0 02-02-2012 01:29 PM
Your throwable type 4 markpierce General Discussion 22 11-12-2011 05:55 PM
Thruster Battery Type? Keith Electrical and Electronics & Navigation 6 02-24-2010 06:22 AM




All times are GMT -5. The time now is 07:56 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012