Displacement Glider, PowerKeel, etc?

For 25' LWL, 6000 pounds displ., and 15 knots.

Mike D's Displacement & Semi-Displacement sheet gives 69 HP.
My Compton sheet only goes to 10 knots at that LWL but gives drag at 571 pounds.
And the Mercier-Savitsky pre-planing sheet gives 724 pounds of drag and 32 HP at 14.3 knots.

View attachment COMPTON2.xls

View attachment MERCIERS.xls

 

Thanks very much for the discussion & response, everyone. Guillermo, thanks for posting your spreadsheet... I can always just use that for comparison.

O.K. - here's my latest version, which has a somewhat arbitrary form factor correction. I'm now hoping it's valid from speed/length 0.1-4.2

I'm assuming the hull is optimized for whatever target speed is entered (in the semi-displacement range, anyway). That's my excuse for my values being lower: it's the hull's fault if it's slower than it should be!

 

More tweaking. Here's the latest.

 

Tad:
I'm not able to open your Compton's spreadsheet...
Also: Who is Mike D? I do not know his spreadsheet...(Excuse my ignorance)

Mercier's results are EHP for hull only. If we asume SHP as being 2*EHP (roughly) and add up to a 7-10% more for appendages, etc., as is quite usual, we would go up to 32*2*1.1 = 70.4 Kn which is pretty close to my 72 HP (Power for 15 kn, somewhat higher than the 14.3 in Mercier's). I'll check my formula against Mercier's for more speeds, size of boats, displacements, etc., to find out how they compare.

Stephen:
This last version of yours seems to be more accurate, in my opinion. I'll also compare it thoroughly against my formula and Tad's Mercier and all three against the older formulas I use at my office. But this is going to take a while as I'm going boating for some days to enjoy the nice (hot!) weather we are having.

Cheers.

 

First cheking, for the same boat:
(Note: Tad's SHP = Tad's EHP*2*1.07)

Speed --S/L--Stephen's--Tad's EHP--Tad's SHP--Guillermo's

7,2-----1,44----10----4-----9-----15
7,9-----1,58----13----7-----15----19
8,6-----1,72----18----10----21----22
9,3-----1,86----23----12----26----26
10,0----2,00----29----14----30----31
10,7----2,14----35----16----34----35
11,5----2,30----42----18----39----41
12,2----2,44----49----20----43----46
12,9----2,58----55----22----47----52
13,6----2,72----60----25----54----58
14,3----2,86----65----32----68----65

I find strange the very big "hump" in Tad's power for 14,3 kn against the one for 13.6

My values for 7.2 and 7.9 kn seem to be high, but my formula is not supposed to work for S/L ratios under 1.8, so those results have to be rejected. Also those S/L ratios (1.44 and 1.58) are well within the "uncertain" zone just after hull speed, where big variations may result for slightly different stern profiles. In my opinion we should work over 1.8

For S/L ratios between 1.78 and 2.14 my formula and Tad's spreadsheet seem to agree quite well. After that it seems to match better with Stephen's, giving both higher values than Tad's. Anyhow, for a preliminary evaluation of speed all three formulas seem to be quite usable, for this length, displacement and range of speeds.

But, going higher:

Speed--S/L--Stephen's--Guillermo's

15----3,0----68----72
16----3,2----72----82
17----3,4----74----93
18----3,6----77----105
19----3,8----85----118
20----4,0----106---132
21----4,2----153---147

So big differences. I find Stephen's increments too low between 15 and 18 knots and then too high after that, seeming the formula is not good for this range.

May it be because over S/L = 3 we are already in the planning zone, and Savitsky's curve is for slender semidisplacement hulls?

More checkings and comparisons in some days, unless Tad or Stephen want to post theirs.

Cheers

 

SteadySailer 58, one opinion

.....this was posted on another passagemaker forum

Let me be the group curmudgeon here... It looks to me like he has the worst of all worlds in this design...

First it is a monohull with a less than 6:1 fineness ratio so 11 knots is just about it, downhill with the engine screaming and a 30 foot following sea curling over the transom...

It has hard chines which makes it quick to rebound roll, and rebound roll, and rebound roll, so he needs both a keel and sail to dampen the motion...

He has the engine shoehorned down in a narrow keel box which has to make maintenance just loads of fun...

He has the initial out of pocket expense and complications of installing and maintaining a large sail rigging while at the same time he has the initial out of pocket expense and complications of installing and maintaining a powerboat engine, wherebye he gets to continuously manage the sails whilst simultaneously burning diesel...

Not to mention the, "wonderful forward visibility", which consists of a 15 degree arc dead forward that is a wonderful view of the aft side of the mast...

In spite of of 831 sq. ft. of sail and a keel stuffed with a cast iron engine, he has to resort to drogue stabilizers to keep from hurling his lunch over the gunnel...

If I were a cynical person I might say I can see why he refused to do the drawings himself and have his name on it... But since I am not, I won't... There is an old guideline I try to follow in life, to whit: Just because you can do something does not mean you should...

OK less sarcastically, all boats are compromises... This one has more than most..

Dennis

 

SteadySailer, a reply

....from that other forum, a reply

I have sailed (and powered) a number of thousands of miles on a boat which has relatively similar dimensions and hull form--but this boat was built 30 years ago and has about 200,000 miles on it--plus has more sail, and a dagger board, which allows the 4'6" draft board up--and enough of a foil and lateral resistance when going to weather--boards up it is a wonderful down wind design, and because of the full buttock sections will actually plane under the right circumstances. It is also considerably lighter, so needs less power.

So I say what Dennis speculates, is wrong in practice, in my experience on this boat at sea. This boat started with a 35 hp engine, which because of the fine lines was enough to drive it at 7 to 8 knots, then a 50 hp engine giving 8 to 9 knots, and now a 110 hp engine--which will drive the boat comfortably at 10 to11 knots under power. The engine is down in the keel, as are the tanks and batteries, as well as ballast. The engines have been tight, but well serviced and lasted about 15 years each in nearly full time service.

The boat does not require any stabilizers--the sails are adequate. The boat does have a relatively quick motion--but this is true of any narrow boat of these lines.

The wide flat keel actually does several things; it gives directional stablity, is flat on the bottom, which allows the vessel to take the ground without toppling over and seems to improve the effeciency of the entire hull form.

In fact this type of long narrow vessel/ combination sail/power is an excellent passagemaker, and I suspect we will see more of these. In fact I am always a bit puzzled that more have not been built in the past. I believe it reflects the manufacturer's pension to stuff as much beam and living space in as short of length as possiable. There are good reasons for this--but not in an effecient passagemaker.

Bob

 

Thanks again, Guillermo and everyone. Great discussion & work!

By way of explanation relative to the Savitsky curve, between S/L = 3.0 and S/L = 4.0 I deliberately chose values between Savitsky's semi-displacement line, which takes off vertically, and Savitsky's planing hull line, which runs more horizontally. My thinking is that a boat targeted for this speed range should still perform well in the semi-displacement range, and would therefore be a compromise in shape, beam, and LCG placement. Above S/L = 4.0 I could probably add a term that would straighten out my curve, but computer programs that predict monohedron planing hull performance with LCG well aft, most based on theoretical work by the same Daniel Savitsky, are already widely available. This is not my area of concern in my present project.

Anyway, in this zone between S/L=3.0 & S/L=4.0 the darkened, composite line on Savitsky's curve indicates that resistance levels off for a boat optimized for the target speed. It's certainly my experience in planing boats that this is real, so it's deliberate (and something I had to tweak my formula to achieve) that my resistance curve levels off here (though at a value slightly higher than Savitsky's for the reason given in the last paragraph).

Having said all that, if Guillermo or anyone else wants to try tweaking my formula to straighten out the dip between S/L=3.0 & S/L=4.0 while keeping those two values, and the ones below 3.0, about where they are, I accept that it would be an improvement, and might have the additional benefit of improving the values above S/L=4.0-4.2

 

This boat is not really a motorsailor, because 48 900 lbs to 831 sqft is not enough for that boat to sail well, not to speak of the big windage that its big upper structures will provide. It is more an assisted sail motorboat.

This boat has two very odd things: first, the Hull material - Aluminium. Steel would be much more appropriate for this kind of boat, but then the weight would be about 70 000lbs. Second, the type of rig: A small main and a big genoa. It seems to me that a bigger main and a cutter rig would be more appropriate. As Dennis has pointed out, a big genoa is the worst sail for the forward visibility.

This boat, unlike a traditional oceangoing motorboat of this size (like the Northhaven, that relies in a superior beam and mechanical stabilizers, to have a comfortable motion) relies on sails to steady the boat. Worst, because after all it looks that the sails are not enough and this boat has to carry a complicated (to operate) stabilizer system with poles.

In the end you gain some efficiency in fuel consumptions, but you have the cost and maintenance of the rig and sails versus the cost of mechanical stabilizers and end up with a lot more complicated system to run (the sails and the poles), especially in bad weather.

As we have seen in this thread:

http://www.boatdesign.net/forums/showthread.php?t=11479&page=10

The difference in operating costs for the same boat (Sturier 40) in the Motorboat version and in Motorsailor version where insignificant between the two versions (for one side or the other), if compared to the initial price of the boat.

I believe that it is also the case here, I mean, any small saving in the fuel waste will be insignificant, regarding the price of the boat.

I don’t understand the advantages of this boat over, for example, the Puffin 58 or the Noordkaper 52, both steel motorsailors with an adequate sail area and a cuter rig, boats that can not only motorsail, but given any decent breeze, can also sail.

http://www.de-gier.nl/createsite/prod/createprod.asp?b_id=6158&page=1&rs_prod_id=3247

http://www.martin-bekebrede.nl/design_detail.php?ID=51

http://www.chuckpaine.com/zsteadysailer.html

What would be the difference in cruising speed while motoring ? 1K ? 1.5K?

That small difference is not enough to justify a bad performance under sail, a worst rolling motion (with the need of stabilizing poles) and a smaller interior space.

As Dennis has said: “It looks to me like he has the worst of all worlds in this design... “

“all boats are compromises” and I would add that these ones don’t seem to make a lot of sense, neither regarding a passegemaker motorboat, neither a passagemaker motorsailor.

 

Tad's Observations on the Power Glider

Tad did have a few interesting observations a few years ago on the Power Glider hull form:
http://www.boatdesign.net/forums/showpost.php?p=14731&postcount=6

http://www.boatdesign.net/forums/showpost.php?p=14731&postcount=9

Whole thread at, http://www.boatdesign.net/forums/showthread.php?t=2545

 

As usual this thread is turning into numerous conversations, hard to keep them straight!

Guillermo, have a fine holiday.
Is any one else having trouble with the Compton sheet above? It opens fine for me in Excell.

Mike D was a prolific and generous early contributor to this forum, back when there were about 6 active members. He passed away a few years ago, but his efforts are still available, do a search.

View attachment disp semi-displ lboatpowercat.xls

On the so-called Steady Sailer, a complete misnomer AFAICT. This appears to be a power boat with auxiliary sails, not a sailing vessel at all. The hull form is that of a moderate displacement shallow vee bottom motorboat with a large volume keel added. Paine did not invent this idea, and I don't think he claims to have. The boat apears to be a copy (slightly enlarged) of Traveller, a boat fairly well known in cruising circles. Traveller was featured on the cover of Passagemaker magazine (vol 1, no 3) in the fall of 1995. There is also a 12 page feature on the boat in that issue. Her hull form is the same as that of the Paine boat, shallow vee with big box keel.

Traveller was designed and built in the late 1980's by a machinist (not a boatbuilder or NA) named Jim Millett. Jim cruised her approximately 25,000 miles and her current owner another 16,000+. Her LOA is 52', LWL is 48', beam is 12.75', draft is 4.5', disp is 44,000 pounds with 10,000 in ballast. power is a 135HP Lehman with 3:1 red turning a 28" by 23" prop. The owner (current, not the original builder) reports a fuel burn of 1.33 usg/hr at 1450rpm and 7.5 knots.

The sailing rig on Traveller is similar to that on the Paine boat except the jib is very small, 112 sq ft with a main of 138 sq ft. The owner reports sailing performance of 3-4 knots in 12 knots of wind, (no angle indicated?) He also stresses that the sails are only useful "under the right conditions" and plans the addition of paravane stabilizers.

Steady Sailer lines


Tad

 

Misnomer

I guess this is a misnomer, but I don't think it was meant to be. The 'sailer' portion of the name being an abbreviation for 'passagemaker'?

From Paine's website description, " The PAINE STEADYSAILER is intended to always have the engine running, so that the yacht travels at a given speed (say 10 knots) at ALL TIMES, no matter the state of the wind. Thus she will make good 240 nautical miles per day, or over 1000 statute miles every four days, no matter what. STEADY speed, rather than the presence of a steadying sail, is what gives this design its name."

Your right Tad. I'm almost sorry I injected items #20 & #21, Payne's Seaknife and the Bladerunner hull forms, but they popped into my mind when Steve mentioned his smaller launch project.

 

Latest spreadsheet / formula attached.

I've included volumetric Froude number and transport efficiency columns. If you go to http://www.proboat-digital.com/proboat/200606/ and select "Pages" at the top, you will find a graph on page 85 on which you can plot these values against what the Donald Blount office considers the "current state of the art."

This revises the comparison to read:

Speed --S/L--Stephen's--Tad's EHP--Tad's SHP--Guillermo's

7,2-----1,44----10----4-----9-----15
7,9-----1,58----13----7-----15----19
8,6-----1,72----17----10----21----22
9,3-----1,86----22----12----26----26
10,0----2,00----27----14----30----31
10,7----2,14----33----16----34----35
11,5----2,30----40----18----39----41
12,2----2,44----46----20----43----46
12,9----2,58----53----22----47----52
13,6----2,72----59----25----54----58
14,3----2,86----65----32----68----65


Speed--S/L--Stephen's--Guillermo's

15----3,0----71----72
16----3,2----78----82
17----3,4----85----93
18----3,6----91----105
19----3,8----99----118
20----4,0----108---132
21----4,2----119---147
22----4,4----133---162
23----4,6----150---178
24----4,8----168---195

I note that between S/L = 3.0 and S/L = 4.8 Savitsky's curve only increases 30% (if that). Against his curve we both appear to be increasing too fast in that range!

 

Stephen,
Not with enough time now (boating), I'll go on working on these matters next week. Nice work on your side. I have to deeply work into my formula, checking it thoroughly (and simplifying it , if possible).
Cheers.

 

Dear All,

I happen to work at Van Cappellen Consultancy and indeed we deal with noise and vibrationreduction for the yachting industry. We have however íntroduced' the steerable thrust tube together with a company called pposeidon into the yacht market for smaal recreational vessels up to 15-18 kts. The idea behind this tube was to surpress noise and vibration from propellers, it also has course keeping advantages, fuel savings and propeller protection capabilities. Look at www.poseidon-pde.nl for details !