San Juan sharpies

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Lopez Mike
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Re: San Juan sharpies

Post by Lopez Mike » Sat Mar 11, 2017 11:06 pm

Wes,
Can I weld aluminum with my regular MIG machine with only a change of wire and gas?

I love mild steel for its malleability and reasonable cost. I just have worried about the sides getting all dented from docking bumps when using thin enough plate to keep the weight down. Also I'm a typical machinist doing welding. Not pretty but I could get my act together.

Another consideration is that wood absorbs a lot of noise. I have a vision of a tin can with a lawnmower engine clanging across the bay.
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Re: San Juan sharpies

Post by DetroiTug » Mon Mar 13, 2017 3:08 pm

Mike,

You didn't ask me, but I'll answer :D

Aluminum can be ran in a standard Mig set up, but it's very troublesome as the aluminum wire is soft and jams easily, heavier wire would work better. It's typically ran in a "spoolgun". I have one, but (for me) it's not as easy as Tig welding aluminum, tig is slow, but it moves slow enough to clean the material as it goes, the mig is much faster and the result is metal balling up on surface impurities. For Mig-welding aluminum, the material has to be very clean at the start or it's a real pain - cleaned with acid. That's been my experience anyways.

For my Tig on aluminum, I had to go to tri-mix (Co2/Argon/Helium) instead of straight Argon. I'm going to give the spoolgun another shot with the tri-mix and see if it's better.

-Ron
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Re: San Juan sharpies

Post by Lopez Mike » Mon Mar 13, 2017 5:59 pm

Dunno why I addressed that question to Wes. Meant it for you.

I have been holding off on getting a TiG setup mostly because of the initial cost. Are there any less expensive TiG machines on the market these days. Surely competition has reared its head by now!

One reason I've been looking more at plywood rather than metal has been that if I mess up with epoxy and wood I know how to deal with it. My welding has given me lots of problems over the years. Self taught and it shows.
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Re: San Juan sharpies

Post by Bob Cleek » Tue Mar 14, 2017 7:35 pm

Harry Sucher's book, Simplified Boatbuilding, The V-Bottomed Boat (with a foreword by Howard Chappelle) has just what information you'd need. It includes plans for a lovely 50' flat bottomed New Haven Sharpie converted to a power yacht which appears very similar to some of the ferries in the Puget Sound "Mosquito Fleet." It could easily be pared down to 35 feet or so. The sailing sharpies rely on their heeling under sail to turn the leeward chine into more of a "Vee keel." When powered, without any heeling (as would the sailing version be when running downwind) that "Vee keel" is just another chine. In a steam boat, I'd expect the slower speed and heavier displacement would be a benefit. It's more when people try to get flat bottoms up on a plane that they'll run into diminishing returns in the hull pounding department.

I've studied Sucher's plans a lot, musing about how it would serve as a steam yacht. The issues that concern, but don't dissuade, me are that the flat bottom, even though it may will have some sheer to the chines, will still require a fair bit of angle to the prop shaft and the prop will be fully exposed and require a good sized skeg to protect it. Additionally, while not a deal-breaker, the greatest advantage of the sharpie hull is it's very shallow draft. In a steam boat where the prop diameter rule of thumb is 10% of the waterline length (if I understand that correctly) would mean than in a 35' hull, you'd be looking at somewhere around five or six feet of draft by the time you were through with hull draft, the prop diameter, prop clearances and the skeg. That's going to limit "gunkholing" in shall water quite considerably.

Not to incite thread-drift, here, but for my money, if welding up a metal sharpie hull, considering the economies of scale in terms of cost and useable hull volume, I'd be tempted to go up to the range of 50' or 60'. Now, I'm not giving a reliable legal opinion here, but I am an attorney and I've read the applicable statutes carefully and I don't think there is really any limitation on length of a steamboat although I've read in several places that the regulations require special inspection and operator licensing for steamboats over 40'. It is true that such regulations exist, but when those regulations are read in the context of the whole section of the regulations in which they appear, it seems that those regulations only apply to vessels which are to be operated commercially. In other words, if one were to carry "paying passengers" or cargo foro profit, the regs apply, but not to what the regulations in other sections refer to as "yachts," defined as vessels used solely for pleasure and not commerce. If I were to consider building such a vessel, I'd check with the USCG and make sure that the 40' regulation limitation doesn't apply to vessels which are not licensed for commercial use.

Another consideration is the engine in such a vessel. Oddly enough, it is often easier and proportionately less expensive to source a larger marine steam engine, perhaps in the 50 HP range, than to source a smaller one, probably because the smaller engines are in greater demand. That said, I wonder whether twin smaller engines, perhaps in the 15 HP range, while probably a more expensive option, might reduce the draft attributable to the prop diameter by half.

If anybody that knows more about it than I do, which is probably everybody that reads this forum, has any thoughts, I be interested in hearing them.

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Re: San Juan sharpies

Post by Lopez Mike » Tue Mar 14, 2017 10:45 pm

Very good stuff. I will be up late looking into the ideas.

One factor for me and perhaps two thirds of the steamers in my area is that we trailer our boats so anything over 25 to 30 feet gets into marginal areas of practicality. Not only from the point of length but from weight. Any boat that gets up towards two tons gets us into special towing vehicles.

The ten percent draft to length rule come close in my boat. Twenty five feet and about two feet of draft. When I am starting out at a relatively high power setting and low speeds I get a fair bit of air being sucked down around the prop. Not cavitation. At my propellor power loading that just isn't going to happen. As soon as the boat gets moving the water under the stern starts to follow the hull and things get smooth.

I suspect that there is little new to be discovered in this area of small easily driven hulls. The need to keep the weight down has been forgotten a bit but maxing out the waterline length is still very important. I'm not sure how much extra drag a hard chine hull has over a fully faired design with compound curves. I suspect not that much.
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Re: San Juan sharpies

Post by fredrosse » Wed Mar 15, 2017 2:05 am

"In a steam boat where the prop diameter rule of thumb is 10% of the waterline length... "
While this represents good practice, it is not a hard and fast rule, the purpose of which is to achieve good propulsive efficiency with a relatively slow turning engine. A boat is certainly a mix of compromises to suit conditions surrounding the machinery and hull. For a large Sharpie with steam propulsion, I would think going down to a propeller diameter equal to 6-7 percent of the waterline length is acceptable. Proper blade area with a reduced diameter can be had with wide blades on a three or four blade propeller.

I am currently planning a 19 foot (waterline length) steamer, very nearly a Sharpie hull, turning a 15 x 18 inch prop at 1000 RPM, with only two prop blades for that boat.

"I'd check with the USCG and make sure that the 40' regulation limitation doesn't apply to vessels which are not licensed for commercial use." I have done this previously, and the US Coast Guard sent me a letter specifically stating that, steam propelled vessels below 40 feet hull length are exempt from the inspection rules, and those over 40 feet would require full compliance with numerous difficult rules and inspection procedures.
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Re: San Juan sharpies

Post by cyberbadger » Wed Mar 15, 2017 3:25 am

fredrosse wrote: I have done this previously, and the US Coast Guard sent me a letter specifically stating that, steam propelled vessels below 40 feet hull length are exempt from the inspection rules, and those over 40 feet would require full compliance with numerous difficult rules and inspection procedures.
That would be mighty handy to have a copy of your letter from USCG or a similar statement from the Coast Guard for other steamboaters in the US...

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Re: San Juan sharpies

Post by Lopez Mike » Wed Mar 15, 2017 3:36 am

I thought that ten percent rule was prop depth to length. Misunderstood.

My overall length is 25 feet and my prop diameter is 1.5 feet. Granted it is a prop designed to absorb a lot of power so the blade areas are very high. The few 18" x 24" props with smaller areas that I've seen have been way out of my budget.

I honestly don't know the waterline length or how to measure it properly. I don't mean how to use a tape measure but whether the length is at rest or at any particular speed. At rest mine is perhaps 22 or 23 feet but at five knots or so it is a lot closer to 25 feet. Is there a convention on this?
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Re: San Juan sharpies

Post by fredrosse » Wed Mar 15, 2017 5:15 am

"....would be mighty handy to have a copy of your letter from USCG..."

I will try to find it,have it somewhere in my library, however I have been collecting steam related books and publications for 50 years now, one of my wife's pet complaints, that I may collapse the third floor with the weight of the books and publications.

Waterline length, "At rest mine is perhaps 22 or 23 feet but at five knots or so it is a lot closer to 25 feet. Is there a convention on this?"
Yes, the effective waterline length has to do with the underway effective length, and that may be,or may not be the length you mention, depending on the buoyancy added with the extra 2 feet you mention.

However, hull speed is taken as a square root function of the effective waterline length, and there is only a trifle less speed calculated using 23 feet vs. 25 feet. The shorter length (23 feet) giving 96% of the speed calculated based on 25 feet. That few percent difference is really not very important in a hobby steamboat.
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Re: San Juan sharpies

Post by Lopez Mike » Wed Mar 15, 2017 5:21 am

I have plotted my r.p.m. v.s. speed and not only is it obvious as to what speed the drag really shoots up, it is obvious on the boat as the stern sinks and a huge stern wave develops. I should now add to that plot the calculated speed/length ratio.

A bicycle speedo made into a tach and a cheap GPS makes for some fairly decent data collection. Assuming reasonable conditions such as flat water, little wind and even less tidal current.
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