Our next boat, LRC Full Displacement.

Nomad Willy · Feb 6, 2014

The power has nothing to do w it.

It's all in the hull.

And there is a grey zone. The 49 DeFever is almost in it.

As I've said before the definitive feature is the QBBL that has been discussed several times. And the relationship between the area of the largest below the WL cross section to the area of submerged part of the transom. Basically if you have more than 3 or 4" of submerged transom w/o a steep QBBL angle it's a SD. Mark's Coot is FD but has a small amount of transom submerged .. For example.

I learned about the QBBL on BoatDesign.net where there was a discussion about this. A specific angle was given and I've gone back to find it but failed.

A 49 DeFever w only one Lehman 120? Finally an underpowered boat. What's the displacement Tom ... Or hp per ton?

sunchaser · Feb 6, 2014

manyboats said:
Basically if you have more than 3 or 4" of submerged transom w/o a steep QBBL angle it's a SD.

So that means Nordhavns and Selenes are SD? I believe I'm missing something in this discussion. A good look at Dashew's FPB lines would suggest FD is of no advantage for MV cruising efficiency. Maybe the term FD has run its course for today's boat designs.

Rather than pontificate, it would appear it is time for our resident expert Tad to chime in.

ksanders · Feb 6, 2014

The problem I see with this whole boat picking thing is that we enter into it with preconceived notions of what we want, with no rational for those notions, then we use circular reasoning to justify them.

Why cant we pick a boat based on a mission requirement instead?

In this case the OP presented a mission requirement. He within his $175K budget, wants a boat that can travel the west coast go through the Panama Canal and explore the Caribbean.

Thats the mission.

What does he need for that mission?

After the mission requirement is satisfied then logically one would start looking at performance and comfort characteristics that we prefer.

Examining these characteristics will lead us to the right boat design, then its just picking a model that best represents that design.

To even think about defining hull form is putting the cart before the horse if you will. The acceptable hull form should flow out of logical analysis, not be a preconceived criteria.

sunchaser · Feb 6, 2014

manyboats said:
A 49 DeFever w only one Lehman 120? Finally an underpowered boat. What's the displacement Tom ... Or hp per ton?

Wet and loaded, a 49 will easily go 59,000 lbs and not eclipse the original WL until above 66,000 lbs.

In this day and age who'd want to install a Lehman as a single anyway, much better choices out there. The perfect and simple single fit, if one were so inclined, for the DF 48 & 49 hulls would be a CAT 3056 or Cummins 220HP reman. The Cat 3056 (Perkins Sabre painted yellow) is in the very nice, new, SD hulled Garcia which has serious blue water chops and has gotten lots of recent press with range above 2500 miles.

Nomad Willy · Feb 6, 2014

What you're missing Tom is probably the QBBL. The DeFevers QBBL angle is too low, narrow, small or flat to qualify the DeFevers as FD. DF probably saw they were very close to FD, much closer than to planing and for marketing reasons made the call.

In your post Tom is the validity of DeFever calling his boats FD the same as the statement that they will last forever?

Four hp per ton is a good Power ratio for FD. I wonder how hard they run their engines and what speed they get?

I'd welcome TAD's input too. Perhaps he knows the specific angle I've been referring to.

psneeld · Feb 6, 2014

And I have posted MANY TIMES WITH LINKS to professional NAs that say the QBBL is only part of the equation...the prismatic coefficient is huge too.

A perfectly flat bottom barge with square front is certainly a displacement object...yet the QBBL angle is zero...meaning it's a planning hull (to some).

Sure if you lightly load it, tip the bow up and apply lots of horsepower...it can plane...hell it can fly through the air like an F-4 Phantom.

But the flat bootm barge has a normal use as full displacement.

So, lets seriously discuss QBBL and what it really means.

Ghostrider42 · Feb 6, 2014

The OP needs to go down to Olympia and check out the Diesel Ducks - without a doubt FD hull!

I just delivered one from Turkey to Uruguay - 6788nm @ 6.5nm/hr used 3000ltrs in 45 days + steadying sails and stabilizers. Steel hull/decks, aluminum superstructure, all wood interior - no veneers, dry stack and keel coolers. For far less than plastic boats with all their gee-gaws.

Ghostrider42 · Feb 6, 2014

Alternate choice is a full motorsailor like a Skookum. Orig built for commercial fishing, they have the best of both worlds. It's my second choice, despite being plastic. There's one in Anacortes, Seattle and Portland - reasonably priced. Why waste the air - use it to your advantage. Ducks are being built as motorsailors too - but they are more expensive.

bshillam · Feb 6, 2014

Diesel Duck, it appears the least expensive is in the mid $300's. Too rich for my blood. Maybe if I ever move aboard full time. Until then I'll scale back budgeting to something within reach.

Ghostrider42 · Feb 6, 2014

Go take a look at the Skookum's.

Underway · Feb 6, 2014

manyboats said:
I learned about the QBBL on BoatDesign.net where there was a discussion about this. A specific angle was given and I've gone back to find it but failed.

An excellent paper by Dave Gerr is on pages 12-17 of the attached publication. Unfortunately, I was unable to extract it without losing the illustrations and graphs, so you'll have to scroll down to get to it. Mr. Gerr discusses QBBL among other design factors in almost layman terms. Worth a read.

View attachment Boat calculations Dave Gerr.pdf

Wxx3 · Feb 6, 2014

psneeld said:
Sure if you lightly load it, tip the bow up and apply lots of horsepower...it can plane...hell it can fly through the air like an F-4 Phantom.

.

Now were talking :dance:

Underway · Feb 6, 2014

More design ratios from Eric Sponberg

View attachment Boat design ratios Sponberg.pdf

markpierce · Feb 6, 2014

manyboats said:
...
As I've said before the definitive feature is the QBBL that has been discussed several times. And the relationship between the area of the largest below the WL cross section to the area of submerged part of the transom. Basically if you have more than 3 or 4" of submerged transom w/o a steep QBBL angle it's a SD. Mark's Coot is FD but has a small amount of transom submerged .. For example. ...

psneeld · Feb 6, 2014

skidgear said:
More design ratios from Eric Sponberg

View attachment 27154

Thanks...one of the MANY NA articles that I have posted in the past when QBBL is heightened to biblical proportions...

here's just one line about prismatic coefficient...

"that performance is closely related to Cp".

while QBBL is important...it's the equivalent to saying that one's looks are solely dependent on hairdo.

psneeld · Feb 6, 2014

markpierce said:

Wow....my boat has nearly THAT much QBBL angle (at least as much as I can tell from TF pictures...even if my chine midships isn't that immersed

...and if Mark's waterline is accurate...I have WAY less transom immersed yet the designer of my boat calls the Albin 40 a semi-displacement......truly amazing....how can pictures lie that much? :rofl:

markpierce · Feb 6, 2014

psneeld said:
...and if Mark's waterline is accurate...I have WAY less transom immersed yet the designer of my boat calls the Albin 40 a semi-displacement.....

Actual waterline is one to two inches below the yellow stripe.

Pushing 14 tons, the Coot's 80 horsepower can't move it faster than hull speed.

psneeld · Feb 6, 2014

markpierce said:
Actual waterline is one to two inches below the yellow stripe.

Thanks...

Mines 5-6 inches less...last owner really was a lousy painter and really screwed up the boot stripe.

As I sit right now, transom is immersed 1 inch at the chine and around 6-8 on centerline.

mahal · Feb 6, 2014

Bshillam,

Did you look at the Cheoy Lee 50 that Ksanders posted a link to? It matches your description of your next boat including price which I thought was impossible. I think it's a lot of boat for the money. Well kept too. What do you think?

sunchaser · Feb 6, 2014

Ghostrider42 said:
The OP needs to go down to Olympia and check out the Diesel Ducks - without a doubt FD hull!

I just delivered one from Turkey to Uruguay - 6788nm @ 6.5nm/hr used 3000ltrs in 45 days + steadying sails and stabilizers. Steel hull/decks, aluminum superstructure, all wood interior - no veneers, dry stack and keel coolers. For far less than plastic boats with all their gee-gaws.

Wow, that is over 8 NMPG and less than 1 gph.

Nomad Willy · Feb 6, 2014

Thanks to skid gear and psneeld we've got lots to look at and/or study. But I don't see the QBBL info. I remember a QBBL on the bottom of a sailboat w lots of rocker. I think it was skidgear that posted It several mos ago.

Anyway remembering hull forms accurately is tricky. Marks Coot looks to me now as it's in the grey area. Not much submerged transom but a flatter QBBL than I had remembered. Looks the same as the DeFevers but w less submerged tramsom.

The Meridian in the post of supposed FD boats is probably closer to a planing hull that FD.

And yes psneeld barges are FD. And yes also that there are many other factors in NA but to be able to tell FD from SD I think the QBBL and amount of sub transom is the easiest to use. The latter being more useful being easier to comprehend. Can you think of another more telling design feature for the purpose?

Underway · Feb 6, 2014

manyboats said:
Thanks to skid gear and psneeld we've got lots to look at and/or study. But I don't see the QBBL info.

The QBBL discussion is in Dave Gerr's paper attached via my post #71. Think it's on page 13 or 14 in the attachment.

cardude01 · Feb 6, 2014

Could be that a Choy Lee pilothouse fits the bill

1977 Cheoy Lee CL-50 World Cruiser Power Boat For Sale - www.yachtworld.com

This is a really nice looking boat!

markpierce · Feb 6, 2014

The photo shows the Coot laying on its keel, thus is nose down. This drawing shows the boat's lines on the level.

The submerged portion of the hull is about three feet deep in the middle.

psneeld · Feb 6, 2014

manyboats said:
Thanks to skid gear and psneeld we've got lots to look at and/or study. But I don't see the QBBL info. I remember a QBBL on the bottom of a sailboat w lots of rocker. I think it was skidgear that posted It several mos ago.

Anyway remembering hull forms accurately is tricky. Marks Coot looks to me now as it's in the grey area. Not much submerged transom but a flatter QBBL than I had remembered. Looks the same as the DeFevers but w less submerged tramsom.

The Meridian in the post of supposed FD boats is probably closer to a planing hull that FD.

And yes psneeld barges are FD. And yes also that there are many other factors in NA but to be able to tell FD from SD I think the QBBL and amount of sub transom is the easiest to use. The latter being more useful being easier to comprehend. Can you think of another more telling design feature for the purpose?

Your "purpose" of "quickly telling by a feature or two" is EXACTLY what the issue is....YOU CAN'T "guess" from a rough pic or two showing a feature or two.....

One design feature without significant info on others is only part of it...even the designers often relent that there's overlap or "compromise".

sunchaser · Feb 6, 2014

psneeld said:
One design feature without significant info on others is only part of it...even the designers often relent that there's overlap or "compromise".

Which is why Dave Gerr's calculations and formulae as posted by Skidgear show the definition of FD to be a calculated number and not a "look."

Like "Trawler," terms and definitions used for advertising tend to get trumped in the real world of NA. A decade ago Dashew said emphatically to anyone listening, "I'm designing an FPB not a FD or SD."

So back to the OP's question --------------.

RickB · Feb 6, 2014

psneeld said:
Your "purpose" of "quickly telling by a feature or two" is EXACTLY what the issue is....YOU CAN'T "guess" from a rough pic or two showing a feature or two.....

Wow ... a serious case of dejavu just set in!

I though we all agreed it took at least 3 photos ... wait, maybe that was to determine the dancing angels per pinhead ratio ... it is all so confusing.

Bob Cofer · Feb 6, 2014

Bry see what you started! There is a boat on G Dock that might fit your needs. Next time we meet up let's take a walk.

psneeld · Feb 6, 2014

RickB said:
Wow ... a serious case of dejavu just set in!

I though we all agreed it took at least 3 photos ... wait, maybe that was to determine the dancing angels per pinhead ratio ... it is all so confusing.

wrong again buster...we agreed you need 3 pics/angles of view to determine whether it's REALLY an anchor ball or not....

RT Firefly · Feb 6, 2014

Greetings,

OK Mr. psneeld. Anchor ball or nut?

Our next boat, LRC Full Displacement.

Guru

Guru

Moderator Emeritus

Guru

Guru

Guru

Veteran Member

Veteran Member

Guru

Veteran Member

Guru

Dauntless Award

Attachments

Guru

Master and Commander

Guru

Guru

Master and Commander

Guru

Guru

Guru

Guru

Guru

Guru

Master and Commander

Guru

Guru

Guru

Guru

Guru

Enigma

Similar threads