ROLL Control pleasure boat

Dauphin,

The Dashews (and by extension therefore, Kelly Archer Boatbuilding) use a roll tank in the Fast Pilot Boat (the "unsailboat"). '

Also, these guys apparently does as well:

http://www.oceaniccorp.com/

(not a boatbuilder, but a "consulting corporation").

Thank you guys for an interesting thread

 

The "Classic Solution " is a delight , If it fit in a container I would by one.
"
So limited headroom, limited roof size, very light building method. No extra weight on top. Up to the point where seaworthiness is in competition with liveability."

The space and other limitations are known , other folks may need a roomaran castle on 38ft , but we are willing to have basically the interior of a 27 ft sailboat.

A tiny bit over 6 ft headroom and a good layout is all that is required .

The hull design should have a bit more depth as we prefer one of the Atkin designd bottoms on the New Jersey Seabright hull style. These have a box keel , which sets the engine low enough to allow a straight out shaft , (about 2ft draft) and is beachable on the keel bottom. These boats also have "negative deadrise" which is claimed to be more efficent . The cruise speeds seems to be SL x 2.8 with SL x 3.3 as an absolute max .

The Parker Cruising speed is 12 to 20 knots. The prototype "Magic" cruises at 19 miles per hour, consuming 4 gallons per hour with a Honda 90, and runs wide open at 24mph..

This is very close to our hoped for 5 nmpg at 18K , the efficiency of a diesel instead of an outboard should do it.

I have not mastered computer design , so am stuck with purchasing a set of plans for a "close" design , and recreating them by stretching the lofting stations , and slimming the width with math , and drawing the resulting boat.

Looks very much like the Classic Solution in terms of interior volume , although the engine is a bit further aft.The box keel also gets the batterys , only 200 lbs , but quite low.

Will your computer easily accept a table of offsets to sketch a boat?

FF

 

Not sure.
http://www.setsail.com/dashew/Stabilization.html
http://www.setsail.com/dashew/dashew215.html
In press http://www.setsail.com/dashew/pdfs/PassageMaker-NovDec05.pdf , they say that filling the flybridge tanks is to target a roll period of 4 second. They do not speak of anti roll function.


But what is interesting is what FF wants look very near 1/2 scale FPB 83.
Length (83ft) , beam (17ft,wl 14ft ) and displacement (30 - 45 Tons) scale.

But when you scale freeboard (estimed around 6,5), it makes a very low freeboard of 3,25 ft for a 40 ft boat. The same for the roof size. At scale, it would make 9 ft long, 2 ft high. Scaling the canoe draft (less than 2ft) will translate to less than 1ft for the 40. I think the low profile is related seaworthiness, but the problem is that human body size or waves height do not scale. At 40 ft, you need comparatively more volume and more seaworthiness. Which is not possible. You will have to forget one, (or make heavy trade off).

And even you hit same problem as smallers. It is not very common to see harness for crew in a + 80 ft boat going barely above displacement speed.

 

You have conflicting figures. You need to choose draft = 2ft OR displ = 8000lbs.

If you boat is 8000lbs, it will displace 8000/64 = 125 cubic feet.
If LWL is 38 ft, and Cp is ,64 (optimized for hi speed displacement boat), you midship section will have to be 5,13 square feet.

If you beam wl is 7 ft, and if the hull form is triangle, the draft will be
1,4 ft. (BTW, deadrise will be 21°).

If the hullform is a flat bottom 2 ft wide, the draft will be 1,1 ft only.


Now, if you want 2ft draft, with a flat bottom 2 ft wide, and 7 ft beam WL, the area will be 9 square feet.
And the boat will displace 9 * 38 * .64 cubic feet = 219 cubic feet. that will weigth 219*64 = 14000 lbs.

14000 lbs instead 8000 lbs, you are likely to need twice the power for the same speed.

 

The classic solution is 10 ft beam. Narrowing to 8 ft will likely cut each passage aside the engine from 1" 6' to 6' only. This beyond of cutting initial stability by more than 2.

If you want to keep 8 ft beam, it would be better to base your layout on the commuter 36 one. But putting an engine box somewhere inside would be a nigthmare.

 

Fcfc,

I stand corrected. However they tried at some point (in one of their blogs) to desable the electronic stabilisers and used the tanks to reduce the roll. I interpreted that as anti-roll, but I see what you mean, and why you differentiate between the two.

 

Could a solution to the engine space be an electric engine and the generator placed somewhere else?

 

The shape of an Atkin SB is rather unique. I measured the revised plan and offer the following .

The plan is for 14 stations 37 inches spacing , the bow is very conventional but about 31 ft from the bow the canoe body ends (a simple transition to the inverted V of the hull aft) about 20 ft from the bow'

The WL beam is 6 1/2 ft and the depth at the end of the canoe body is 18 inches. The aft 8 ft or so of hull has very little contact with the water , mostly at the hull sides , the V tunnel top is actually above the waterline at rest.

The beam at the bottom widest part of the box keel is 3ft, which should be enough to allow sitting on her own bottom either on a trailer or taking the tide.

As the box widens to fair into the hull there is room to work on the engine , and even room for a V engine if needed. about 4ft at the top of the box.

With no planometer it is hard to get the displacement ( & very long with graph paper!)'

The budget would not allow the experimenting with an electric drive engine , and we have no "house loads" that a simple 55a alt. wont handle.

The std diesel like a Yanmar LH 4 and a 2 speed ZF transmission is fairly compact and has far higher efficiency than the diesel/electric as they work today.


FF

 

I understand what you want is something shallow draft,at any price.

I suggest your read the figures for "Summer Kyle"
http://www.gerrmarine.com/power_50.html
http://www.gerrmarine.com/images/boat_images/power/gerr42tunnel/gerr42tunnelC.GIF
http://www.gerrmarine.com/images/boat_images/power/gerr42tunnel/gerr42tunnelD.GIF
http://www.gerrmarine.com/images/boat_images/power/gerr42tunnel/gerr42tunnelA.JPG

The speed is 11 kts with 210 hp, very very very far of the 35 kts of the "Classic solution", with 250 hp.

Given the stern design, buttock angle are too steep to allow greater speeds. Robb White design was OK to go faster because it had something less 4 inches draft, as Atkin Rescue Minor design. Scaling it to 40 ft would mean less than 8 inches draft. You are asking for more than twice. it is not possible.

The volume of the keelbox also translate to heavy weigth.

Narrowing it by 1/3 to bring beam to 8 ft will not cut weigth by 1/3 because you still want a wide bottom. The "Summer Kyle" is 20 000 lbs. So you are targeting around 15000/16000 lbs and you are looking around 150-170 hp (7.5 8.5 gph) to go 11 kts. You will also severely cut stability as with narrowing the "Classic Solution".

 

The Summer Kyle was an unsucessfull interpition of a concept the designer did not understand.

Atkin refined the design over 40 years and 50 designes , DG attempted one that had little resemblance to the published work of any NJ Seabright Skiff.



While its no light weight the boat sucks air at speed , keeping the speeds down to poor performance at best.

With its low freeboard and huge cabin glass the Atkin "River Belle" is a reasonable example of the Box Keel + Reverse Deadrise concept , in a 35 ft cruiser, for inshore work.

With higher freeboard (about 5 ft foward) the hull volume begins to be suitable as a cruiser.

The River Belle was the source for the underbody (scaled up in length and down in beam) and Stroller (Herrishoff) the source of the sheer and profile,.

What do you figure just a 30 ft very slender canoe body 3 ft wide at max beam with 4 ft wide 18 inches up would displace?

Thanks,

FF

 

The Dashew vessel scales down to quite close to a box boat dimensions.

Another , made for even higher speeds is this Maryslim

http://www.luxist.com/2007/03/30/maryslim-yacht-launches/

Which if scaled down by half would also fit in a box.

The displacement would only be 1/4 of Maryslim 18 tons and the engine would be vastly lighter than an 1800HP monster.

Both the Dashew boat and Maryslim are designed for crossing big water at high speeds , with similar draft (in scale) to my proposal.

I don't understand how they can get away with ocean work , and the same boat scaled would be restricted?

I can understand they will have a vastly superior ride in larger waves , and an ability to carry on far longer , but how is the stability compromised by scaling down?

FF

 

REFOLO ASD

Loa = 6.00 m
Power = 1 x 225 hp DP Volvo P.
Speed = 42.0 knots

No roll at all...heeling angle at full speed while turning = 4 deg.

 

Imagine a 8 lbs weigth at one end of a 2 ft arm.

The moment to the other end is 16 lbs.ft.

Now, scale it 1:2.

length are 1:2.
surfaces are (1:2)^2 = 1:4
volumes are (1:2) ^3 = 1:8

Your 2 ft arm is now 1 ft length.

Your 8 lbs weigth is now scaled to 1 lbs. (density is the same, and you have scaled the volume by 1:8 ).

Now you moment is 1 lbs . 1 ft.

By scaling your drawing by 1:2, you have scaled your moment by (1:2)^4 = 1:16

The righting moment of a boat is nothing more than a moment. And so is scaled power 4 of the scale.

See how R/C sailboats model have enormous ballast and draft not at scale at all : http://www.hobby-lobby.com/nirvana.htm

 

In offshore fishing Dory hulls were used at sea , and were considered seaworthy. Most are long and slim , although the ride was claimed to get better with a ton of fish aboard.

The depth of the proposed boat could be deepened (the box keel narrowed) and a slim 6 cylinder like the Iveco 150 lowered a few inches.

I know engines are are heavy , but not dense , about 1300 lbs with transmission.

Would an extra 6 or 12 inches of draft help with self righting?Assuming an intact covered deck.

FF

 

From a few years ago was this comment on the O1 discussion.

"For my high speed short range cruiser, I'd go with "Needle Senior". LOA 55', DWL 49' 4", beam 8', displacement 9,000 lbs. It will cruise at 35 knots on 300 HP and with her 55' length it would slice through chop much better than a shorter boats. I'd change the open cockpit to an enclosed Pilothouse and change the jet drive to a surface drive. With an 8' beam Needle Senior would meet the trailerable width requirement but would exceed the allowable length in most states. I'd design a gooseneck trailer and extend the bow up over the neck to minimize the trailer length."

The proposed STROLLER II would be 16 ft shorter but only 6 inches narrower , so should be almost as stable as the NEEDLE SENIOR.

MY goal is 8800lbs ,so if the N-S was 15 ft longer at 9000lbs , that should be doable.

Not sure there would be a weight savings as the only engine I can find that is mechanical injection is the IVECO 150 , that is Tier 2 and Euro 3 legal.

DG might have selected a lightweight M-5 rated engine like a BMW / Yanmar conversion , that is probably as heavy as the Iveco , and 2-3X as powerful.

FF