Low Length/Displacement Hulls

Photo of hybrid planing/canoe body powerboat test model. L/B of canoe keel is about 14:1 carrying 70% of displacement. This fits in there somewhere.

 

Dave Gerr has an article about efficient powerboats in the latest "The Masthead: The Journal of the Westlawn Institute of Marine Technology". http://www.westlawn.edu/news/WestlawnMasthead17_Mar.11.pdf
He includes his own formula for maximum hull speed/length ratio which is based on the D/L ratio and is never less than 1.34.

 

What a coincidence. My issue of The Masthead was waiting for me this morning and I planned to read it at my leisure later today. I think I'll read it sooner than later.

Regards,

P

 

Tom,

Your attachment looks very intriguing. I guess you are about to undertake another water towing series of tests, as you described at your website for the original Bluejacket? One term used in the UK is "Swim". See Hadar Narrow boat.

The other attachment is one I cannot attribute. It is not mine, but I had saved it quite a while ago, to assist & remind me in learning about hull forms. I hope the designer will identify themselves here. Might it be PAR? This hull form has been discussed at length in this forum. Remember these brilliant threads.

http://www.boatdesign.net/forums/powerboats/help-economical-semi-planing-designs-16746.html

http://www.boatdesign.net/forums/powerboats/displacement-glider-powerkeel-etc-12512.html

http://www.boatdesign.net/forums/boat-design/displacement-speed-question-27879.html

From acorns, oaks might grow:!::?:

http://5magazine.wordpress.com/2010/09/08/superyacht-ra-by-adam-voorhees-design/

Regards,

P

 

P - I do believe that was one of mine from quite a few years ago... an early iteration of the hullform that I coined the name "monomaran" for. It is essentially the same hullshape as Malcom Tennant developed to avoid squatting in displacement catamarans, and is also similar the one that Tom is now working on. Indeed there is another variant faetured in the same edition of the Masthead, which was my entry into the recent Proboat design comp... though that one (Sliver) was a rather more extreme development of the idea - really more of a stabilised monohull.

Tom - Glad to see you're moving ahead with your work on the Glider... I wish I could find a little time to do the same! My own version (of this type) is similar, albeit with the canoe body faired more into the chine up forward in an effort to reduce slamming. It'll be very interesting to hear the results of your testing....

A number of others must have been watching also, for a I have recently come across a number of craft with similar underbodies - the most recent being the new Azimut Magellano 50. A less extreme example of the idea... but surely a reasonable example of proof of concept!

 

Will,

Thank you very much for putting me right. Monomaran is a great name. Those ProBoat competitions are very thought provoking.

Mike Storer wrote about a similar hull form some time ago. Scroll down.

http://www.storerboatplans.com/Solarboat/solarboat.html

Regards,

P.

 

Scoop them all up, stick 'em in a bag, give it a shake and what drops out? A boat with a box keel...
Proof that there is rarely really anything truly new in boat design...

 

EMF posted this at the forum, but there were no replies.

http://www.boatdesign.net/forums/attachments/boat-design/4280d1129182433-first-attempt-draft.jpg

 

Will,

Good grief, your design just appeared again, as I Googled "displacement glider".

12-07-2003, 04:44 PM
http://www.boatdesign.net/forums/boat-design/displacement-glider-2545-2.html

The Alsphere website appears to have disappeared.

http://www.epicos.com/Portal/Main/H...If+VJak6DbhPebAlN4/36w+EfT9ZkpsLliXoDGTHVBm8h

 

Beauty is in the eye of the beholder.

Narrow, longish, heavy, ownership in doubt, probably rolls on a wet lawn. Built just so, in order to cruise rivers without a wash, so as not to upset anglers and disturb nesting wildfowl. A fine stem to part the waters with nary a splash. A stylish buttock to leave no wake. 2.2 BMC diesel, probably frost damaged. Perhaps the antithesis of the subject of this thread. Needs a miracle.

Never look at "project" boats:!:

P.

 

An Option

Dear Pericles,

Please, for your comments.

http://www.ocea-yacht.fr/pages/okeanis.html

 

Yikes... that was back in 2001.... how time flies...

 

I've read that one and it makes not too much sense to me. There are generally accepted indicators of relative speed: FnL (or just Fn) and FnV. Second one is called volumetric Froude number taking in account weight of boat and is used for high speed displacement, semi-planing and planing craft. Say, FnV<1 is displacement, FnV=1...3 is semi and FnV>3 is planing mode.

Using common terms in naval architecture, there is absolutely no need to invent SL Ratio (that itself is analog of FnL) with correction to DLR. One can just use FnV instead.

Systematic series suitable for resistance predictions for type of craft in question (de Groot, NPL, SSPA, 63, 64 and others) are using FnV as indicator of relative speed. So why do we need modified SL Ratio??

 

Will, seen Your design. Looks great!

We were also working on power-saving concept, but this is for combining of cruising mode and planing mode, for 100' motoryacht. This one:

 

Will,
Saw your Sliver again on the Masthead as well as the earlier page on Graphite. How long have we been looking at this canoe keel concept? Wish someone would fund some boats that really exploit the idea. One reason I don't like the box keel term is that it is already in use to describe boats that don't get very far into the basic concept of the separate keel/body philosophy.

Pericles,
You have kept a good record of past ventures into the canoe keel and I will add that list to the files.

The reason my model hull has the wide chines forward that it does is that it must offer good accommodations in the forward cabin in a boat of trailerable length. A longer and softer bow shape would be easier on wave entry but I'm interested in practicality of the principle. I made the model without much softening of the shape forward to first test this shape with the objective of being able to soften it a bit later. The model mirrors the chine of the Bluejacket that it will be compared to in the tests to give a better baseline of comparative results.

Frankly I don't think slamming will be much of a problem at the intended speeds and that only moderate shaping will be needed. The boat is intended to run in level trim at all speeds (even more level than Bluejacket) and this should control slamming to a large degree. Bluejacket runs at 2 degrees trim which maxes at top speed and is all bow rise with zero squat at any speed. Even flat bottom hulls don't slam when run level in chop at moderate speed. Its all in the incident angle that the water meets the hull bottom.

The model has been sitting about for a while waiting on both me and a suitable test vehicle. Hopefully this Spring.