SCALE MODEL , Size?

I think FF dreams of something like below:

But he wants it also be capable of:

NB : 5 nmpg at 18 kts means 3.6 gph, roughly 72 hp for 18 kts.

and of course enough volume and loading capability for extended cruise.

 

Here are the hull lines of the River Belle , both the origonal at 8ft 10 in beam , and computer slimmed to 7ft 6 inch beam.

The hull will be higher (added freeboard to 5 ft at bow, and the sheer fancied a bit.) She was origionally designed to be planked , so would be simple in metal .

 

You should be aware of :

Source : http://www.douglasbrooksboatbuilding.com/rescue.html

Source : http://www.boat-links.com/Atkinco/Oar/Unsanctioned.html

Source : http://forums.bateau2.com/viewtopic...postorder=asc&highlight=rescue minor&start=15 second message

 

FF
Is this one better. I did not recall the draft so set it at 16" roughly to scale from your drawing. At this draft it displaces 4 tonne.

It looks like a canoe under water so should be easily driven. Michlet shows 44kW at the hull at 17.5kts. Would translate to about 100HP at the engine. She is well into semi-planing at this speed so Michlet may not cope well.

Rick W.

 

"Michlet shows 44kW at the hull at 17.5kts. Would translate to about 100HP at the engine."

That is close to what we were hoping for. (75 hp at 18K).

Atkin claimed these hulls were very efficient , my own guess was that the accelerated water from the forward sections is trapped in the tunnel section ,using energy already "paid " for.

The ability of the hull to NOT have the stern sink , due to the prop accelerated water under the afterbody also probably helps.

One Atkin that was overpowered began to bow steer at top speed , Atkins cure was bow chine strips to lift the bow.

I hope to avoid the problem by using trim tabs aft that can actually recess if needed at top speed.

100hp with a mechanical injected engine costs under 5gph , and gets 20% better IF I could convince myself to build an unrepairable (by me) boat.

Probably will stick with mechanical.

Thanks for the help , does your program give surface areas?

I would love to know the areas of the hull and deck , so I can figure if the all up weight can be held to 8800lbs.
The DREAM is 200g fuel tankage , 60 water, 20 waste , but reality may intrude.
EZ enough to cruise with partially empty tanks most of the time , and accept a speed / mileage penalty when long range is required.

Thanks,

FF

 

FF
I prefer metric units. Area is 40sq.m = 430sq.ft without any deck.

If the hull was 1/4" steel it would weigh 1.88t. Just the plate - no bulkheads.

The performance is dominated by wave making so things happen that Michlet does not cater for. Your model testing would validate the accuracy.

I also looked at what is the most efficient hull for this speed, length and beam. It is a narrow catamaran. A 4t version requires 29kW on the hulls to do 17.4kts. So say 65HP at the motor/s. The individuals hulls are 28" maximum beam so large enough for bunks and a motor in each but does not have the usable volume of a single hull. Depends on what you want to do.

Rick W.

 

The drawing you posted is getting really close!!

The box keel on the Atkin would end 5 to 5.6 ft before the transome.

Thats what forms the "reverse deadrise" and perhaps gets the claimed great efficiency , and prevents the stern from going down under way at speed.

430 SQ ft is great as the heaviest layup envisioned is 3 lbd per sq ft.

3/4ozm,24ozWR,3/4m,24WR3/4m, 3/4AIREX repeat on other surface.

Aluminum was in the running , but the Iveco 150 is claimed (by the Iveco dealer) to be Tier2 and Euro3 compliant , with mechanical injection.

Thanks for the help!

FF

 

FF
I will be very interested in any model testing you do.

If you build a model then post some photos and I will redo the hull more accurately. Give you a Michlet prediction before the actual testing.

The 1/6th scale model should require about 7lbf to do scale speed (7kts) if I am close.

Rick W.

 

RW

I am new to this board and have read a lot of posts about River Belle. I am also considering it for electric power, but I have no interest in taking it above its Hull Speed. Have you worked out what the drag would be at say 6 knots in purely displacement mode ? That would give a better idea of the motor sizing required for my purposes.

Also, why did you convert 44Kw required at the hull to 100hp at the engine ? Wouldn't that be 58.6 hp'ish ?

Thanks

Alan

 

Alan
The 44kW was the actual power required to push the hull through the water. You have to allow for prop efficiency, motor auxiliaries, appendage drag, windage etc. and then to convert to imperial so it is in language Fred can relate to. Hence around 100HP.

If you are looking at a solar boat then you might be interested in what I am doing. There is a post on this:
http://boatdesign.net/forums/showthread.php?t=19972

The boat has evolved a bit since then. Displacement has gone to 1100kg, length has come down to 12m, 1.8m maximum beam, design speed is 7.5kts with 1.5kW, top speed will be around 11kts, achieve 5kts with 500W, 6 X 210W solar panels, 1 X 1kW wind turbine and 11kWh of batteries, 48V system. A preliminary rendering is attached. It will be built using glass composite.

A 6 knot boat would be around 24ft long and the beam depends on how much stability you want. The narrower you make it, the less power required.

I can get Godzilla to give you a hull shape if you specify what is required but it will not be until the new year.

Rick W.

 

Hi Rick

Thanks for you comments re HP - that makes perfect sense.

On the other issue, I was particularly interested in a Mundoo III style vessel for river cruising, but given the low water levels at this end of the Murray, was drawn to the River Belle because of its shallow draft. The hull shapes are very similar except for the tunnel stern and they are much the same length.

Atkin specified 80hp to achieve 13 Knts in the River Belle, but at this speed the hull would be planing, which isn’t necessary for my purposes. The original electric Mundoo uses a single ETek motor and cruises most efficiently at 4.5 Knts using about 2Kw and I think that River Belle should perform just as well.

However, I think I need to know the low speed drag figure for the River Belle hull shape before I can decide if its really viable, and was hoping that you might have some ideas?

Cheers

Alan

 

Alan
I will have a look next weekend. If you have a link that shows the hull design you have in mind I can draw it up and check. If it has a clean stern it will not have much wave drag - just viscous drag and using Michlet should give reliable result.

I was looking at the Etek but have almost settled on a Perm PMG-132 with a sevcon 4Q drive. The Perm is rated at 4.8kW on 48V and will run to 9kW for 10 minutes or so. These are slower reving than the Etek and I can get away with a 2:1 reduction and still swing a decent prop. If you are happy to travel at 4-5kts you would do OK with solar power and a few batteries.

I am going to make a little drive leg for the Perm motor. I will post a drawing when I have finished it. You might be interested. You could probably produce a drive system with panels, batteries anf the leg for under AUD10,000. I expect it would be competitive price with a small sail drive and you do not have to keep buying fuel and carrying it around.

Rick W.

 

Thanks Rick - it is the same hull you were doing some work on for "Fast Fred" earlier in this thread (Messge #17), although I will use the original wide beam version (8'10") not Fast Fred's narrowed version, so perhaps you have it already drawn up (almost) as per your attachments to Message #19.

My concern with the Perm-132 is that it has brushes. That represents a maintenance issue of not only having to buy and replace brushes regularly, but having to remove and dismantle the motor periodically to polish or skim the commutator.

There are some other issues with brushes as well such as arcing and audible and electrical noise that I would prefer to do without. However, it is frustrating because the do have a higher voltage handling and power output than say the MARS motor at 6hp continuous (15hp max). On the upside, the brushless motors are considerably simpler, have no moving parts (aside from the actual armature) and are considerably cheaper to buy. I'm considering two MARS motors in tandem which will cost about the same as one PERM-132 although I would have to spring for an extra controller, but it has the advantage of a "limp home" mode should a motor or controller fail, and under normal cruising conditions of course, the power consumption would remain the same.

With the setup I have in mind, I am fairly sure that I can cruise for 3 or 4 hours per day in sunny conditions almost indefinitely without running the generator at all - ah bliss.....

Anyway, thanks for your offer to have a look at the drag figures, I'll look forward to your findings with great anticipation!!!

Cheers

Alan

 

A big delight with motors with brushes is they will still give a good output with lower voltage.

So if you overestimate the vessels range , you may be able to power on with mostly dead batterys , beats rowing!

FF

 

That's an odd thing - have you any idea why that might be the case ?

Alan