View Full Version : ROLL Control pleasure boat
FAST FRED
08-14-2007, 12:46 PM
I know this section is usually a discussion of ultimate stability , "how far can she roll and still come up?"
I would like some help on concepts of roll stability for comfort.
The hull is a NJ "Seabright Skiff" which is claimed to be a good offshore performer, the design a modified Atkin with box keel and reverse deadrise.
The hoped for cruise speed of 15 -20K precludes "flopper stoppers" or paravanes from too much drag.
Std fin roll control as well as the new gyroscopic are just to pri$y for me.
A few power boats have used dagger boards as a roll control, I would be delighted to install a center board ,even with an active trim tab , if that would work.Grounding would cause no hassles.
The negative deadrise could use individual stern trim tabs for roll control, if they could take the work input , and would have enough force.
An article I recently read claimed the US Navy used rudder input to control some roll, but it was unclear if the vessel had a single or more than one rudder.
Any references to this would be appreciated.
Comments?
FF
USCGRET/E8
08-14-2007, 06:49 PM
Older boats/ships had bilge keels. The newer CG 110' Cutters have fins that are contolled by a computor.
Doug Lord
08-15-2007, 06:55 PM
FF,I like your daggerboard idea. If you could try this on a model it might be a worthwhile experiment: how about a daggerboard in a trunk that functions like a gybing board. When the force of the roll pushes the front of the board over it would counteract the roll! It would require experimenting to see if the thing would just oscillate or not. You might have to experimentally vary the pivot point which could just be a slightly raised portion torward the back of the board(looking down from the top). It might require some sort of centering spring? I made a gybing board one with a "V" block in the front end of the trunk: the "V" would fit over the leading edge of the board to prevent it from gybing or it could be slid forward to vary the range to which the board could gybe each side. Seems to me it might be able to be made to work....What do you think?
kengrome
08-16-2007, 02:29 AM
Hi Fred,
Anything you stick into the water is going to create more drag and therefore reduce efficiency. I would think that because of this, you might want to focus on the use of a steadying sail or auxiliary sail rather than any additional appendages that will run in the water.
Sails work great for roll control, and they increase rather than decrease your fuel efficiency. They are "low-tech" so they won't require high cost computer controls either.
If designed innovatively with a special mast, you could have a sail that rotates into position as a big sun shade or rain tarp when you're moored rather than cruising. A tabernacle would be a 'good thing' for passing under bridges and such too of course.
It seems you may be interested in a more high-tech solution than a sail for roll control. On the other hand, anything you try OTHER THAN a sail is only going to reduce your fuel efficiency -- and isn't fuel efficiency one of your primary goals in this boat?
FAST FRED
08-16-2007, 08:35 AM
"On the other hand, anything you try OTHER THAN a sail is only going to reduce your fuel efficiency -- and isn't fuel efficiency one of your primary goals in this boat?
True , but at 18K the wind is almost always forward so far that nothing but aerodynamic drag would be created , along with the drag from the weight of mast , rigging et all.Plus it hardly fits with a Commuter hull shape , and is more junk to assemble , disassemble and ship.
A gybing center board would be far easier to use , esp if it self tended.The form drag of a few sq ft is worth .1K to keep the crew happy.
Probably a control of some sort would be required , even manual would be fine as a rudder bar hooked to the control point would be OK. The boat will be operated offshore (as needed) however long overnight passages are not contemplated for cruising.
If the speed can be maintained , our 50 to 100 mile days should be quickly done in daylight.
So 3 questions remain on this design , the fore and aft location of the proposed board to stabelize her.
Weather a more efficient shape of box keel than the simple one used by Atkin , better shaped leading or trailing edge? outside to NCAA 0010 or ?
And the final question of weather an aluminum hull & deck (not my first choice ) will protect a modern electric controlled engine from a lightning strike?
FF
For the daggerboard, I do not understand what will bring the daggerboard centered when the rolling correction will be enougth. As for me, a spring wont do it, because the force will be dependant of the speed of the boat, not of the roll angle.
For using rudder instaed of fins, I am note sure. Because I fear main of the cost of a stabilizer system is the control logic and the actuators. The fins by themselves are not the expansive part.
And the first problem I see is when you will want to use an autopilot. Coupling roll control + yaw control on a single gouvern will lead to very pricey controls.
The only thing I see that MAY lower costs are electronic advances. Mems gyros : http://www.analog.com/en/subCat/0,2879,764%255F801%255F0%255F%255F0%255F,00.html may lower the cost of control logic. And electric driven fins may be cheaper than hydraulic actuated ones. See http://en.wikipedia.org/wiki/Electric_power_steering. Hi power low voltage electric engines do exist for the later.
The negative deadrise could use individual stern trim tabs for roll control, if they could take the work input , and would have enough force.
FF
Using trim tabs for active roll and pitch stabilization is becoming quite common and is very effective (and efficient..since trim tabs actually improve the L/D of most planning hull designs at low-to-mid cruise speeds). Cost is an issue..the smallest vessel that we have provided this type of system for is 57' LOa and was a rather expensive 57-footer at that..roughly 3.5 million total cost. (The owner likes his bells and whistles..;-) We dis install a set of active tabs that worked very well on a 37' Deep-V demonstrator craft, but the installation was anything but sanitary or permanent.
All that said, we have had under development for about 2 years, a transom stabilizer solution based on interceptors instead of trim tabs and using integrated electro-hydraulic actuators that only require DC power (existing systems all require hydraulic PTO or electric-driven pumps, reservoirs, servo valves, etc). We have been installing large active interceptor packages for many years (USN X-Craft, for example) , but recent advances in servo technology are allowing us to head down-size with the concept, making it affordable for even boats i the 35-40 foot size range.
But we are still about a year of so away from fielding the systems commercially. And....interceptors do not work as well as trim tabs at lower speeds..below, say, about 25 knots..and so are more suited to go-faster boats. An all-electric trim tab solution is not in the cards right now..trim tabs require too much force relative to interceptors and thus still require a decent hydraulic power installation to be active for stabilization. The set of trim tabs we are currently installing on a 63' planning MY require about 14 HP, as an example, and get that from a pump mounted on one ofthe tranny PTO pads.
What kind of roll control would fit on that style of boat ?
http://www.cnsco-silure.com/Francais/Mer/LovStar40/Lovstar_40.htm
http://www.rangeboat.com/index.php
http://www.classic-boats.com/en/fiches_tech/Andr12en.pdf
Cruise in the 11-15 kts, top around 20 kts.
What is the break even point between trim tabs and fins ? (Although a hydraulic system is a nogo on this kind of boats).
And whatabout pneumatic systems, like http://www.gyrogalestabilizers.com/index.html if electric only are not powerfull enougth ?
What kind of roll control would fit on that style of boat ?
http://www.cnsco-silure.com/Francais/Mer/LovStar40/Lovstar_40.htm
http://www.rangeboat.com/index.php
http://www.classic-boats.com/en/fiches_tech/Andr12en.pdf
Cruise in the 11-15 kts, top around 20 kts.
What is the break even point between trim tabs and fins ? (Although a hydraulic system is a nogo on this kind of boats).
And whatabout pneumatic systems, like http://www.gyrogalestabilizers.com/index.html if electric only are not powerfull enougth ?
If you cannot use hydraulics..then how could you use a pneumatic system? Both require some form of PTO or electric motor to operate the pump. The gyro-gale system is not really any different than Wesmar and the others except for the pneumatic drive..and the benefits of that are all marketing hype for the most part. A rate-based fin stabilizer system is a rate-based fin stabilizer system and there are a number of good options out there. Vetus recently introduced a novel and comparatively inexpensive fin stabilizer package for smaller vessels that was actually developed by Koop (formerly KoopNautic).
The boats you pointed links too would all be compatible with an active transom trim tab solution as a better alternative than trying to fit 2 or four fins, even at the lower curise speeds..but the requirement for a hydraulic power source to 'wiggle' them remains. There is not a breakeven point, per se..its more a matter of lifting area and it is often easier to install oversized trim tabs than it is oversized fins, to deal with lower speed control requirements.
Vetus recently introduced a novel and comparatively inexpensive fin stabilizer package for smaller vessels that was actually developed by Koop (formerly KoopNautic).
I checked Vetus price list. The inexpensive :D system (without the hydraulic pump) is more expensive that the main engine + gearbox for above boats. (volvo D3 130 or yanmar 4BY150).
The boats you pointed links too would all be compatible with an active transom trim tab solution as a better alternative than trying to fit 2 or four fins, even at the lower curise speeds..but the requirement for a hydraulic power source to 'wiggle' them remains. There is not a breakeven point, per se..its more a matter of lifting area and it is often easier to install oversized trim tabs than it is oversized fins, to deal with lower speed control requirements.
It was my understanding that fins were better than stern flaps. Fins (if submerged) work either side, but only the down flap is working. (a single fin can make the boat roll both side, but a single flap will only make the boat roll one side). Fins are also further of roll center than transom flaps. So better efficiency. Also fins are somewhat compensated. So less power to activate, or faster move.
But there are no fins systems for "small" boats, so there may be problems somewhere.
Agree there are really not any 'cheap' solutions for smaller boats. Some of the key system elements just don't 'scale down' in price.
Trim tab systems are often more effective than fin systems, despite their 'one-sided' force-producing nature, because we can often fit a larger lifting area tab than can be obtained with a fin. Fin areas are limited by their span exceeding rub rail or keel in most cases. It is true that fins require less power to operate than do trim tabs.
What would the the order of magnitude for trim tabs "wiggle" power for boats above ?
When you look at autopilot for same weigth boats, (with tiller), they do not use more than 150 - 200 watts.
Order of magnitude?..at least 10 HP. There is no comparison betweeno the autopilot requirements and those of an active trim tab stabilzation system. To achieve good stabilization performance means having real-time tab position response be a minimum of 5 times faster than peak unstabilized roll rate of the vessel. Thus 25 degrees/second or better is not unusual for fin or tab deflection rates..which takes horsepower.
10 hp :eek:
That 7500 Watts.
Even with a 30 % mech efficiency : 2500 watts.
As fas as I remember the work of a force of 1 N moved 1 meter in one second is 1 watt.
That you need to move 25000 N over 0.1 M in 1 second.
That you move 5600 lbs over 4 inches in 1 sec.
Or 2800 lbs over 4inches in 0.5 seconds.
That's really huge. You are speaking of forces around a quarter / half the weigth of the boat.
Another misunderstanding from my part.
When a boat roll, there will be a moment between Center of Boyancy and Center of Gravity. All forces are vertical.
But with a roll induced by a fin. One force will be perpendicular to the fin. But what is the other force, and with what application point ?
Pericles
08-30-2007, 01:53 AM
FF
A post elsewhere in this forum directed me to http://www.loganboats.co.nz/index.html
Jib sail and bilge keels on a very good looking vessel. Worth a look. Read the log of the Cadenza as she crossed the Irish Sea from Wales to Ireland.
http://www.vetus.nl/en/index.php on pages 26 & 27 have their own hydraulic stabilisers.
Pericles
How is determined (or approximated) this point ?
Stabilizer fins should should be aligned with that point to have the best efficiency.
But from what I have understood, small move of boat (roll or pitch) are around CF CoG of Waterplane (of course variable point). And inertial forces are around CG CoG of boat ?
Not speaking of added mass effect / hydrodynamic damping.
FAST FRED
09-09-2007, 07:56 AM
Using tabs has far more appeal than active fins that can be damaged,and cause extra drag.
This boat will have trim tabs , as the reports of using high speed on these hulls suggests too much stern lift and bow steering.
The question then becomes one of response time, electric , hydraulic or pneumatic.
AS the boat will have a Hyd system for on board tasks , I would assume the solenoid controls used on autopilots on boats with full time pressurized hyd steering would be simplest to adapt.????
FF
FAST FRED
10-06-2007, 05:34 AM
It would seem that a small trim tab bump to raise one tab , or lower the other ,should be able to keep the boat more stable in a beam sea.
The effort to effect a light weight ( under 8000lb) very narrow (7.5ft) boat at speed should be far less than a 3-1 L-B boat weighing many tons.
What does an "interceptor" look like ?
Since electronic control seems to be a huge portion of the cost. I would have NO problem with an antiroll "Joy stick" or old fashioned aircraft rudder pedals.
The lowest cost version would not be trim tab based, but could be a direct swivel of a balanced "center board" , which could be retracted for beaching or non rolly courses.This could be built for a few hundred bucks , rather than thousands.
How would the location of the center board be optimized to reduce roll?
FF
fish4life
10-06-2007, 11:15 AM
Years ago I was at a commercial boat show in New England somewhere. I was checking out this builders boat models when I came across his answer to rolling. He had a box about 16 high 24 wide and the lenght was as wide as the cabin roof. The box lenght went from side to side acrossthe cabin roof.
Inside the box\tank was three baffles with drain holes. The box\tank had enough water in it, about half full to soften the roll when the water was tring to drain to the other side during the roll.
What do you think.... never saw anything like it again
Beware I am not engineer at all, even less marine.
Seems that a anti roll device should be able to heel a boat 4° to 5°.
So the effort on fin like device should be righting moment at 4-5 ° heel / lever arm of the fin.
Righting moment is GM*sin(heel)*displ. for low heel angle.
lever arm of the fin is approx middle span of the fin to somewhere between CF and CG (Section view).
So for normal fins, for same righting moment, the narrower the boat, the greater the effort on the fin.
Now, for lighter boats, there is minimum righting moment to reach (heel during turns, offset loads, wind + vawes). So lights boats increase GM to get some stability. (Form stability (GM term) for light boats, weight stability (Displ term) for heavier ones).
So the effort on a fin on a narrow light boat may not be that smaller than the effort on a heavy beamy boat.
Next, instead of speaking of effort, it would be better to speak of power = effort / time.
As BMcF said, fin period (one stop to the other, then back to first stop) should be 1/5 of boat natural roll period.
T (roll period) = 0.44 * B / sqrt(GM).
So the narrower the boat, the higher the GM, the quickest the roll period. Again a light narrow boat will need much more power to move fins, because even if the effort is lighter, he will have much less time to do it.
Some numerical application:
Disp = 8000 lbs. Bwl = 7.5 B=8 GM=3
4*200 lbs people on the same catwalk will make heel the boat 8°.
Roll period = 2 seconds.
That means fin period = 0.4 s : one stop, to the other end, back to the first one.
Expressed other way : fin middle between the two stop : should reach requested postion within 0.1 seconds.
For comparison, an electric autopilot is 4s for full stroke : 8 sec for full period. A antiroll device for that application need to be 20 times faster.
Electronic is not the cost. as said, mems gyro is 30$, and a 5$ microcontroller will fit. The software programming for a PID control is an exercise for first year automation student. What I have not checked is the finding of the natural heel of the boat. Maybe the natural heel is where the average displacement of fin is centered on the neutral position of fins. Also there is an issue with very long period of rolling, such as quartering seas, when the boat is slighly faster or slower than the waves.
The real cost is the actuation mechanism:
Say the fin move between -10 + 10° 0° is neutral.
the fin is neutral:
the microcontrol will say:
go to +8° : 0.1s to do it.
go to +6° : 0.1s to do it.
go to -7° : 0.15s to do it.
back to neutral : 0.1 s to do it.
NB For interceptors, see http://www.maritimedynamics.com/interceptor.pdf
You can also go a bit further in stability preliminary estimation:
Say Lwl = 36 ft. Bwl = 7 ft, disp 8000 lbs.
You can have BM = Cwp^2 * Lwl * Bwl^3 / 12 * disp
Cwp Waterplane coefficient around .75 (rather full)
That should give you BM aroud 3.5 ft. (optimistic)
B = estimated 1/3 D (D canoe draft).
D = disp / Cp * Cm * Lwl * Bwl
Cp = hi speed powerboad = 0.64.
Cm = Midship coefficient = somewhere around 0.6 = between triangle(.5) and ellipse. (.78)
D = 1.5 ft.
B = 1/2 ft below waterplane.
BM = 3.5 ft, GM = 3ft (previous post).
G = around waterplane = well ballasted sailboat, not powerboat.
Preliminary estimation of G for a powerboat would be around mid freeboard.
Assume 3 ft freeboard = rather low freeboard.
G = 1.5 ft above waterplane.
Now GM = 1.5 ft.
Recompute the heel
Now the heel with 4 people on the catwalk around 15° . GM approximation may be out of range.
Heel angle with 2 people = 8°.
Rather tender boat, you should seriously analyze stability if you want some moderate offshore capabilities.
4 ft freeboard would give GM = 1ft : serious analysis of sailing uprigth capability to do.
NB virtually ALL powerboats have engines and heavy weigths in the bilge. Mid freeboard CG estimation is for theses conditions. You may think of adding lead ballast in the very bottom bilge or in a long keel like older sailboats. But you will have to build VERY ligth to have a displacement of 8000 lbs including engine weigth, and still have allowance for ballast. Heavy engine wont fit : Typical engine 3 ft heigh will have its CG around or slightly above waterplane (D Canoe draft = 1.5 ft). Not low enough.
Another possibility is increasing waterplane Beam. you gain stability, but you loose containerability, decrease powering efficiency and motion comfort ration (bigger waterplane for same displacement).
Roll period = 2.7 second.
You fin should now move in 135 millisecond, instead of 100 millisecond. Not a big change.
FAST FRED
10-08-2007, 04:58 AM
Thanks for all the help.
I wonder if with a roll period of only 2 seconds! weather the hull would simply "surge (rise) rather than have time to roll?
If so the simple nonpowered centerboard might give enough roll resistance for the time it takes for the hull to lift , rather than roll.
Yes the boat will seem really tender dockside , but that concerns me far less than the ride quality.
The hull will be based ob one of the Atkin box keel, reverse deadrise hull styles , which seem to have a good reputation for a seaworthy, seakindly ride while underway.
Inside the box\tank was three baffles with drain holes. The box\tank had enough water in it, about half full to soften the roll when the water was tring to drain to the other side during the roll."
I think these are known as Fram or surge tanks.
I know of the concept , but the interior volume is so tiny with a 7.5ft beam I would be reluctant to loose much room, and the water wont have much time to get from side to side , if the roll period is 2 seconds.
FF
I wonder if with a roll period of only 2 seconds! weather the hull would simply "surge (rise) rather than have time to roll?
You are confusing things. The natural roll period is something inherent to the boat. It is not the rolling period of the boat in waves. The rolling period in waves is of course the period at which the boat encounter waves.
If the boat is hit abeam by waves with a 10 s period, the boat will roll with a 10 sec period. As the wave period is very different than the boat rolling period, the boat will gently follow the wave slope at twice the angle. For normal waves 1/13 heigh / wavelength, it will heel around 10 ° each side.
If the wave period comes nearer the boat natural roll period, things becomes nasty. The heel will be much more than twice the wave slope. up to 4x or 6x. because it will enter in resonant rolling.
And if your boat, 7 ft Bwl, 2s natural roll period meet abeam a chop 2 sec period, 1 ft heigh, 13 ft wavelength, it will ROLL nastily, probably throwing things inside due to the roll speed, and the helmsman will probably change heading within minutes for more comfort.
Yes the boat will seem really tender dockside , but that concerns me far less than the ride quality.
FF
Offset heeling hangle is used by ISO as a way to assess seaworthiness of small boats in ligth conditions (Category C and D less than 40 ft). Before speaking of ride quality, you will be more concerned by floating uprigth in most wheater conditions you intent.
mydauphin
10-08-2007, 07:27 AM
Years ago I was at a commercial boat show in New England somewhere. I was checking out this builders boat models when I came across his answer to rolling. He had a box about 16 high 24 wide and the lenght was as wide as the cabin roof. The box lenght went from side to side acrossthe cabin roof.
Inside the box\tank was three baffles with drain holes. The box\tank had enough water in it, about half full to soften the roll when the water was tring to drain to the other side during the roll.
What do you think.... never saw anything like it again
These work but only on large vessels. The tanks are tuned to vessels roll frequency, the neat thing about then is that they work at anchor. The calculation on these is complex and they require a strong structure to hold weight. Do you remember boat builder?
FAST FRED
10-09-2007, 05:04 AM
"you will be more concerned by floating uprigth in most wheater conditions you intent."
Indeed the boat will be expected to make a few offshore , or long shore passages to be able to visit the Med and beyond.
My readings suggested the long narrow shape would help the seaworthyness and sea kindlyness of the boat , and I was planning on no basic restrictions on travel.
No the North sea in winter wasn't on the plan, but being caught out in a 50K thunderstorm , or making (uncomfortable) progress an 8ft sea should be doable.
Can these hull dimensions be used for these conditions? With the 1300lb engine in the box keel I would have assumed the CG would be low enough.
I do expect the boat to be tender when in port , and to move a good deal when walking on the deck.
IF it proves too uncomfortable simply securing , mechanically and firmly the dink alongside should solve much od the motion.
FF
Indeed the boat will be expected to make a few offshore , or long shore passages to be able to visit the Med and beyond.
My readings suggested the long narrow shape would help the seaworthyness and sea kindlyness of the boat , and I was planning on no basic restrictions on travel.
I fear you do not uderstand what your figures mean for the boat. You should really try something like Freeship, or other design tools, to draw hull lines and check some basic figures with your expectations.
FYI, a 40 ft 10ft beam 8000 lbs looks like : http://www.classicsolution.nl/frameset.html
http://www.stadtdesign.com/images/products/608-7-0.jpg
You see how low profile is the boat, and the very limited surface where you can stand up (around the engine only). And even then the headroom is limited to barely above 6 ft. No mast, no antenna, no radar, nothing on top.
It has a waterline beam around 9 ft. Trying 7 ft would mean narrwing the boat 2ft. Just imagine the photo without the catwalks. In previous post, I said initial stability is proportional to Bwl^3. 7^3 = 343 9^3 = 729. So narrowing by 2ft, you just cut initial stability by more than two. Very significant.
Another with the right beam, but a bit shorter and lighter is: http://www.parker-marine.com/interiorcom36.htm
http://www.parker-marine.com/descom36.htm
You will note the designer said of his boat : "It should be born in mind that standing headroom is limited to 6' in the cabin (as designed), and cannot be increased more than 1". "
Imagine now lengthening it 10%. You have now a 39ft boat weighting 6600. Add now 20% in depth to the underwater part of hull. Your boat will now weight 7900 lbs and will have a draft of 12 inches + 20% = 14.4 inches of draft.
You now have something like 40ft long, 8ft beam, 8000 lbs boat. Are these boats seaworthy ?
bvisailman
10-11-2007, 11:14 AM
I am looking at Used trawlers like Island Gypsy, Marine Trader, and Albin. I am wondering whether what would be more stable in rough seas? A twin screw hull or a single screw hull design?
Could someone please send me an Email at: baskew9859@aol.com if you have a reply to this question.
Thanks!
Perhaps I have been a bit rude in the previous post, but I really suggest to play a bit with a design tool. Current computer design tool can give you in real time the displacement and BM. They may lack features for designing real things, but are very good for a preliminary design.
You will see how shallow draft is a hull when you target Lwl 40 ft , Bwl 7 ft and displacement 8000 lbs. This shallow draft forbid to put the engine deep down. We are speaking there of canoe draft around 1 ft, 1,5 ft. The engine will be above bottom, at least to access oil drain. The bottom and keel themself will have some thickness. So the engine CoG will likely be ABOVE waterplane.That a bit hight to be useful for righting moment.
So the only way to give these boats some seaworthiness, is not to put weigth down ( no way, no deep enough ), but it is to remove the maximum of weigth on top. So limited headroom, limited roof size, very ligth building method. No extra weight on top. Up to the point where seaworthiness is in competion with liveability.
For your size, these boats cannot match category A: They will lack by far the required righting moment of 25 kN.m. That would mean a GZ of 0.70m , on hull where half beam is 1.00 m. No go.
They will probaly pass category C. but C is under what you request. Top limit Force 6 wind (27kts) and 7 ft waves.
Remain category B up to Force 8 wind (40 kts) and 13 ft waves. But then it need extensive calculation and cannot be told with just a few figures.
PS : I remind that CE / ISO norms are not a classification society. It is just the bare legal minimum a boat must technically meet to be sold on the EU market. Real classification society have rules much stricter than CE / ISO.
DanishBagger
10-12-2007, 01:43 AM
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 :-)
FAST FRED
10-12-2007, 05:04 AM
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
...
The Dashews (and by extension therefore, Kelly Archer Boatbuilding) use a roll tank in the Fast Pilot Boat (the "unsailboat"). '
...
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.
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.
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 a delight , If it fit in a container I would by one.
....
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.
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.
DanishBagger
10-12-2007, 06:54 PM
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.
DanishBagger
10-12-2007, 06:59 PM
Could a solution to the engine space be an electric engine and the generator placed somewhere else?
FAST FRED
10-13-2007, 05:31 AM
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".
FAST FRED
10-15-2007, 05:38 AM
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
FAST FRED
10-17-2007, 04:34 PM
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
RANCHI OTTO
10-17-2007, 05:05 PM
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.
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
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
FAST FRED
10-24-2007, 05:25 AM
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
FAST FRED
10-24-2007, 04:03 PM
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
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