Micro Cruiser

Thank you.
Now, when the calculations of hp per (metric) ton are done, is torque, gearing and prop size/style taken in consideration? I've read of 5hp motors(slow speed diesels) pushing 20K lb boats. Pretty sure they had a large diameter prop, no idea on gearing or type.
The Sabb mentioned before would fit the bill, I think.

 

everyone here has said the same thing, buy a smaller low cost boat first (22ft to 25ft tops) for very little money, learn a lot, sell it, and then do your large voyage with a larger boat. After some time sailing you wont be on here asking daft questions.

Forget about this generator stuff, its bollocks.

Can you motor across an ocean with a little outboard and no sails? yes... technically. The boat that did it was tiny, he drank 1 litre of water a day, and his cabin was tiny. It does however give an indication that modern outboard motors are quite reliable. I personally much prefer 2 stroke, as they are simpler. In europe they have pollution regulation and am not sure if 2 strokes are allowed anymore. The boat that crossed the atlantic with a 2.5hp tohatsu

http://www.tohatsu.com/news/seiko.html

 

They are allowed if they pass emissions tests. Only the direct injection ones can make it, so all small engines are fours. Commercial users could still buy new "third world" carburated smokers, but sales volymes are too small for import.

 

Better ask the stupid questions first vs making the wrong choice
It will have sails for sure. And it looks like I'll be investing in an OB for backup.
Appreciate the help, and reality check.

 

Thanks for demystifying the colloquialism (it's always nice to run across other people who use that term, http://rurudyne.deviantart.com/art/Colloquial-Grammar-Legal-Usage-110476254 ).

I would imagine that the varied power requirements for diesels vs gas has to do with the fact that they are higher torque/lower RPM which affects the prop selection, with the very biggest ship diesels turning at only about 100 RPMS, IIRC, a speed that precludes the need for any reduction gearing and the associated loss of power, however slight.

I would also imagine that the effect would be even more pronounced with steam where full torque is available from almost the start and max RPMs are usually lower still.

Now about being overpowered: I guess it's like cars that can go fast but are usually stuck in traffic (the programmer that came up with Doom used to hot rod Ferraris for a daily driver, go figure) those HP numbers sell. I kinda like the idea (for a non super-yacht ordinary well off folks can afford) of either electric or hydraulic (with a CPP) powered by two diesels (as applicable) of the same family, using common parts, but different powers, providing three distinct speed ranges without having to worry about under loading the engine or running a generator out of its happy place (if electric).

On the Bolger, or something like it, 20 HP for maybe 10 kt would make for a great boat for skulking about. To get even better economy I'd go with a small diesel, burn waste grease or biodiesel, and supplement it with hydrogen generated from a solar powered water fuel cell, using metal hydride storage (doesn't explode). Because the burning agent promotes full combustion of injected fuel emissions go down and grease/diesel use goes way down while maintaining or increasing power.

Incidentally: niiiice boat.

 

About Power

AI see some people indicating what I consider a rather large amount of power for slow speed operation, and in my experience with low powered craft, one can get fairly close to hull speed with about 1.0 to 1.8 horsepower per ton of displacement.

I have built two such propulsion arrangements, and the power numbers are real, it has been my job for more than 40 years to know about power, as a mechanical engineer, initially in building submarines, and in the utility power industry.

I bult an electric cruiser from a 14 ft O'day Javelin sailboat, running a 24 volt motor. That boat, with 4 adults aboard, could do 5 MPH for several hours using about 0.6 horsepower. The motor is rated at 3/4 horsepower, and it turned a 14 x 17 three blade prop at 400 RPM. Power is measured as volts x amps x motor efficiency, no guesswork here.

My steamer has the handicap of paddlewheel propulsion, and a very slow turning engine (50 - 60 RPM Max), producing well under 1 horsepower in normal cruising. Weighing in at 1 ton actual displacement, it makes 4 MPH and has cruised all around the eastern USA. Paddlers are horrible in rough water, propulsion efficiency drops very low, but I think this discussion is only about submerged screw propellers.

I would be very comfortable in a small boat having 2 hp per ton, provided it had a proper propeller (big diameter, low RPM)

 

Tohatsu TLDI outboards are accepted in the EU for commercial use only. If d1970 were to claim he was a deep sea fisherman or an ocean liner for one, who knows what shennigans would ensue?

http://www.tohatsu.com/tech_info/tldi_faqs.html

http://www.ribs.co.uk/outboard-moto...lehr/commercial-use-2-stroke-outboard-motors/

 

Fred,

Might that not be influenced by having a boat that, to borrow a phrase, is floating like a butterfly, of actually low displacement relative to length?

I'm referencing the fact that having a high LBR isn't the only way to reduce wave drag, but also having a high beam to draft ratio too can be useful, that these should be cumulative (and moderation in both should help keep surface area low).

I believe it's been humorously suggested that you can get a Bolger Tennessee moving by taking a whiz off the transom and the Wyoming is still very light (the 50 HP power suggestion in that link is doubtless because it's for use as a planing craft and those always need more ponies, but 50 isn't really much ... the Azumet 55 has heavy stuff and lots of space and needs maybe 20 times more power).

 

Lbr

LBR = Length to Beam Ratio?

I do not have experience with the factors you mention, but please shed some additional light on the sibject.

The O'day is just a common 14 ft LOA centerboard sailboat, converted to inboard power (centerboard well cut out, shaft/prop installed, bilge keels added) and total cruising displacement is about 1200 pounds running with 4 adults.

The steamer I have weighs 2150 without passengers, so typically 2500 to 3000 pounds total displacement. It has essentially a New Haven Sharpie type hull, 20 ft long, 5 ft max beam (4 ft wide bottom), and 8 inches nominal draft. Hull weight is much more than I wanted, but I keep adding things. Next modification will be a bigger boiler and bigger engine, might even go all the way to 3 horsepower!

Thanks in advance for information.

 

Wonderful. One HP per Metric ton of displacement sounds much better.
The Fisher 25 is roughly 5 tons. Thus 5 Hp turning a decent prop slowly
should be interesting. Not as big as I'd like,since it will create drag under
sail. Would a 12 inch prop create too much drag for this type of vessel?
Thanks lads

 

As I understand it the wave system of a displacement boat, while principally dependent on the length of waterline (the infamous and useful "hull speed" concept), is still either strengthened or weakened by the form of the boat. The mass of water is pushed both to a side and under the bow, and that which has been pushed under reemerges as a secondary wave some distance along the hull.

Here is one discussion of the bow wave I knew how to find: http://www.ivorbittle.co.uk/Article...he bulbous bow for my site This one again.htm

Now what I think, relative to what I know, is that the reason a boat with a long length to beam ratio affects the strength of the wave system has something to do with the primary wave while the beam to draft ratio has to do with the secondary. In both cases the boat would be pushing more or less water out of the way depending on how favorable these are or aren't.

The wave system itself is still stretched out along the length of the hull, but as it is heavier in the case of a fat, deep boat it is a greater impediment to progress. Likewise, pushing less around results in the ability to go relatively faster without starting to climb out of the wave system.

There seems to be minimal difference up to a SLR ratio of 3 or 4 to one, but thereafter things start improving for the slender displacement boat.

Now, it is commonly stated that as SLR goes up to 20 the increase in surface area results in diminishing returns; however, the BDR (which I've encountered fewer statements about) tends to get worse in such instances too.

It seems to me that same should hold true if a boat was freakish in the other direction too: very wide and shallow ... whatever benefits are had for the latter the surface area is huge. Of course with the exception of a few Russian warships, IIRC, not many boats with a LBR of 1:1 seem to have been built no matter their draft (those warships weren't low draft boats even if their BDR may have seemed lower).

This brings up why less may have been said about BDR: that in many cases it really is just if the boat has a deep or shallow draft and how that directly affects the weight of water being pushed around.

My own thoughts is that a moderately narrow boat with shallower draft will have the similar resistance advantages as a narrower/deeper boat of the same length and displacement, and have better form stability or ease of laying out accommodations, just at the price of blue water suitability (I'm more interested in riverine use anyway). It was the madness behind the raised deck cruiser, um, cartoon in my gallery