The perfect 10 knot boat/Lowest Cost per Mile?

Good points.

I question the propeller. I don't see a need for variable pitch. Feathering/folding yes, but not controllable as in constant shaft RPM. What benefit do you see that I don't?

 

New Age Trawler/Motorsailer; Kite assisted PowerYacht

How about an 'economy model' of this kite-assisted power trimaran?
New Age Trawler/Motorsailer; Kite assisted PowerYacht
http://boatdesign.net/forums/showthread.php?t=20319

Back to those design concept drawings by Humphrey’s (attached PDF). I can fully imagine a scaled-down version of this tri-hull design, in the 65-70 foot range, with a wonderful rear ‘swim’ platform deck incorporating a sportfishing arrangement and/or a Scuba diving platform. Just inside could be a tender stowage as shown; or rather a complete diving & fish tackle facility. The tenders could then stow up on rear deck, or one forward, one aft.

The power would be a single main engine sized to develop the vessel’s desired top speed, and it could transmit this power by conventional shaft/prop arrangement, or with a azimuthing Volvo IPS dual prop unit, or via a retractable azimuthing Rim-Drive prop unit, or a simple chain/belt drive unit....

 

The point I see in this you can get the just that constant shaft RPM assisted with the sails and the max fuel effiency.
Or when desirable the max speed like running away Gustav

 

"Feathering/folding yes, but not controllable as in constant shaft RPM. What benefit do you see that I don't?"

ALL diesels like to run heavily loaded for longest life and best efficiency, regardless of the RPM chosen.

With a CPP and sail assist you can set advance speed , observe the EGT and optimise the load easily by cranking the pitch.

Weather the sail is making 90% of the propulsion or none, the engine can be run loaded , its best condition.

This works for all engine speeds , so when powering into head seas , that too can be done at highest efficiency.

The difference between a well loaded engine and a poorly loaded unit making the same HP cam be a 60% or greater increase in fuel consumption.

FF

 

And what if ...

The engineering, manufacturing and material costs of a super efficient boat would cost MUCH MUCH more $$$$ than you ever spend in fuel bills in a normally efficient current boat

Current boats are already fully optimized for their intents. The manufactuer can earn some money building them, the customers can afford to buy one, use them, and get some enjoy using them.

If you build a technically super efficient boat, say like solar powered car, but bring the same reward to customers using them as solar cars are useful to day to day drivers, you will just loose a big bunch of money.

People do reduce their fuel bills and costs. Instead of buying a V8 gas powered ski boat, they just buy a PWC. Not an ultra slow wet narrow rowing skiff converted to power that could keep them water skiing.


You spoke of 3000 nm at 10 kts at lowest cost. OK. So the safety and comfort provided by ocean rowing skiff or minitransat is acceptable. No other constraints.

 

New Boat, Cost, Size, Return on Investment

First off let me say that boats are not often good 'investments' as far as return on invested amount...but then again that is not necessarily why we buy or build new boats.

I will point out that there are probably quite a few multihull buyers over the past number years that may well end up making a profit on their boat investments or maybe breaking even...and on larger vessels as well. The price of building a new vessel has gone up so dramatically in the last few years that the price they paid for their present vessel may well allow for them to make a profit upon sale.

You might also take into account there are a 'limited' number of good used multihulls on the market and these are generally all priced below what a new one cost to build...and yet sometimes more than what the original buyer paid. So he has gotten some good enjoyment out of the vessel, and sold it for close to what he paid....maybe minus his operating and maintenance bills...still not a bad deal.

Then look at the huge price Tom Perkins has spent on a 'really different' vessel, Maltese Falcon, and he has just taken on a partner who likely paid for his share the entire investment that Perkins had made...not a bad deal.

I believe someone could build a nice version of the kite-assisted trimaran I suggested....maybe even in epoxy-saturated wood construction...maybe over in low wage market such as Philippines, Thailand etc,...and sell for a profit down the road when fuel prices will most certainly be MUCH higher. ...and in the meantime have a lot of fun with the project

In fact I venture to say I could sell one tomorrow, IF it were already built. Buyers in the market now (at least those that really have the money NOW) want their vessel 'yesterday', not neccesarily a year or two from now.

 

You are right. I didn't state all the constraints that I thought were implied. Passage making to me implies relaxed, comfortable cruising.

Cruising means different things to different people. Most people would not describe 12 days driving a mini to a 10 knot average as cruising.

 

If you add comfort in the game, there is no issue.

The nordhavn 72 http://www.nordhavn.com/72/overview.php4 is probably the best selling 3000nm @ 10 kts boat. It is built since 2004, and builder claims to build 4 a year. Over 10 sold would be a fair claim.

On the opposite, the FPB 83 http://www.setsail.com/dashew/do_PARADIGM.html , while technically a much better performer (6300 nm @ 11.3 kts), has NOT sold a single sistership, despites its press coverage.

Both boats are in the 4 Millions $ ballpark. (Prices may be some years ago)

So, although ordinary people, absolutely unable to buy a FPB 83, may find this boat very comfortable, the ones who really have the money must find it lacks MANDATORY features a 4 M$ boat MUST have (such as crew quarters I guess, I do not really know, I am very very very far from having 4M$ to spend in a leisure boat), and find the fuel burn issue much less important. Otherwise, that boat would have sales.

Now, if you still want the minimum boat 3000 nm @ 10 kts, with comfort more or less on par with the price, that should be something between FPB 64 http://www.setsail.com/dashew/FPB64_intro.html 4700 nm @ 10 kts and passagemaker lite 56 http://www.passagemakerlite.com/designs/passagemakerlite-56 1700 nm @ 10 kts. I would say at least one million $ for a professionally built with expected equipment.

NB both minimum boats sell less than the bigger N72. And will probably sell much much less than the N52 / N55 despite smaller nordhavn products have lower performances for a similar price range.

Perhaps, you can save a few more gallons going lighter, http://www.nigelirens.com/FRAMEMolly.htm http://www.tuco.dk/admin/bib_img/_mgl0949120608154717.jpg . Note this boat is not intended to do ocean passage. You will certainly severely reduce comfort going light. But not that much the price because light building technics like Corecell sandwich with infused epoxy are not cheap building methods.

It is about less than half the weigth of the FPB 64 but same length. So half the fuel burn for the same speed is not too far. So 1700 gal instead of 3400 gal. And reduce range from 4700 to 3000 nm, so 1100 gal would fit. That should make around 3.5 tons of fuel in a 15 tons hull. Doable, but expect to put ALL your passagemaking gear in a small bag. A passagemaking version based on hull lines and displacement will probably match 3000 nm @ 10 kts with avery good nmpg, but will be a boat where the comfort available onboard will not match the building cost (or where the ones accepting the comfort will be unable to pay the price) , and hence will not sell. Like the FPB 83.

 

Fc...

All reasonable points, comfort is important to those going offshore for pleasure.

Dashew mentions a half-load displacement for the FPB64 of 75,000 pounds, Irens published a full load displacement for Molly Ban of 36,700 pounds.

Molly is designed for coastal cruising (short term) and carries only 1000L of fuel. Water tankage is not mentioned. To go offshore in Molly add 5000+ liters of fuel, substantial fresh water, ocean going structural modifications, ocean cruising gear (anchors and chain, etc), stabilizing gear, and owner's items for long term living aboard. This will increase weight considerably. I doubt a 64' ocean cruiser could be ready for sea at less than 50,000 pounds. Of course this increase means more fuel, and so it goes.

 

http://www.boatdesign.net/forums/bo...motorboats-11479.html?highlight=power vs sail

 

Gerr's revised hull speed formula

Do you have the source of Dave Gerrs "revised" formula? I have been aware for a long time that the SL of 1.34 is a theoretical figure and that is very conservative for long,skinny or light boats but I would be interested in seeing whre or how he came up with this calculation.

Cheers

Al

 

Hull speed is a defined parameter solely based on the waterline length of a hull and the gravitational constant. It is the celerity of the lateral wavetrain of the hull with wavelength equal to the hull waterline length. The formula for celerity is:
V=sqrt(g x Wavelength / (2 PI)) (g is gravitational constant 9.8m/s/s)

If you use British units for length and speed then the constant is 1.34.

Rather than use some less than ideal concoction of this basic relationship there is very accurate software available for predicting hull drag for slender hulls. It can be downloaded free from here:
http://www.cyberiad.net/michlet.htm

There are many users of the software on this forum able to help you get started. Once mastered (read the manual) it is very simple, fast and accurate.

The notion of hull speed is not really relevant to slender hulls.

Rick W

 

Gerrs hull speed formula

Hi Rick

Thanks for that and I understand about the relationship between gravity, density of water and the length of the vessel, but I am sure that Dave Gerr also understands this and he must be considering other factors if he has published another method of calculation, as posted by RHough.

I would like to some support for the idea before I use it in anger.

I also realise that slender hull forms are not really subject to the SL 1.34 paradigm, but that leaves a huge area of ignorance between "normal" hull forms and "slender" hulls. When I read of Gerrs revised formula, it occured to me that he may have done some work in this area and found an algorithm that applies.

I have done a couple of designs that exploit slender hulls efficiently ( I built a 28 foot alloy diesel cruiser to work at SL's of 2.6 to 2.8 a few years back) and
I am very interested in developments in this area.

We have far too many pleasure boats with beam/length ratios of nearly 2:1 that seem to need 100 SHP per tonne to just go fishing at Rottnest.


Cheers

Al

 

Good points. And while the FPB 83 hasn't sold any sisterships, the FPB 64 are apparently selling like hotcakes- last I heard, they've started joinerwork on the first one, the second hull is well underway, and there's a couple of years on the waiting list to get one of the later hulls.

Part of that may relate to the issue that, even though the 83 is a four-point-something million dollar boat, it really doesn't have any more space than a typical 55-60' trawler. It's a sea boat, and from what I've heard, a good one- but it seems the people who have that kind of money to toss around just aren't biting on a boat designed for a couple to live on and handle by themselves. Hence the cheaper, single-diesel 64. (Still worth an order of magnitude more than the average house, though.... so no-go here!)

As far as efficient cruising at 10 knots- well, for sheer cost efficiency, I think you'd have a hard time beating a Wharram cat. Maybe give it saildrives instead of the deck-mounted outboard, and you'd have a half-decent motorsailer. They have their quirks and their detractors, but there's a few thousand of them out there, and you can have one ready to sail for less than the cost of the CF mast and mainsail for a modern racer/cruiser type, and about the same as what the engine and driveline alone of the FPB 64 costs.

 

If you are interested in design of slender hulls then you should take the time to learn Michlet and its hull optimising component Godzilla. It takes all the guesswork out of the hull design and produces reliable results based on analytical solution of the wave drag.

I can tell you from my experience that formulas based on empirical analysis of data sets are ordinary by comparison with Michlet.

Rick W