Has anyone ever seen or used a "planing trailer"?

[rbgarr]

I've been reading Lindsay Lord's "Naval Architecture of Planing Hulls" (1946) and came across this interesting idea:

'From extensive experiments by Elco, it has been determined that the planing hull, unlike the displacement craft, can tow a planing trailer with but negligible added resistance, provided the trailer is fitted to the boat. That is, with a trailer of identical section shape as the transom of the main hull and coupled a foot or so aft of it, the trailer planes on the wake of the main hull without adding appreciably to the original wavemaking resistance. Such a trailer adds only slight wetted surface friction.

The Elco trailers taper from the beam of the transom to a point about as far aft as the trailer's width.... The speed reduction is around 3 to 4 percent for loaded trailers.'

Apparently these trailers were used for extra fuel or cargo carrying capacity.

[Mike Field]

That does sound an interesting idea, Dave. Does that tapering go right down to zero, or to a smaller transom, do you know. (They didn't have any drawings you could post, I don't suppose? http://media5.hypernet.com/~dick/ubb/smile.gif )

[rbgarr]

There is a drawn illustration, but I don't have any scanning capability. It shows a rounded tapered trailer coming to a point, sort of like the stern on 'Baby Bootlegger' (if you know what I mean?). There are no details on how, or how rigidly, the trailer is fixed to the main hull transom. I'd think that would be critical to know how to do, as I imagine the twisting action in any kind of seaway could be problematic.

[Tom Lathrop]

Some designers are adding small additions to the sterns of powerboats nowadays to add a bit of performance by modifying the wake slightly. Don't think that is what Lord ahad in mind though. When I saw the idea of the trailer, I thought Lord had departed a bit from his usual good reasoning.

No doubt the thing would work under some conditions but it doesn't look like a very seaworthy system. Maybe he intended it for use by the military like the dropable fuel tanks on aircraft, to be discarded if unfriendlies were run into. He was working on PT Boats at the time he wrote the book and they were known fuel hogs.

I've read the book and some parts several times. It's, by far, the best book going on the subject. I wish someone as qualified as Lord would update it. In 55 years you'd think that it might have been done.

[This message has been edited by Tom Lathrop (edited 12-17-2001).]

[DougWilde]

Other planing texts I've found useful are:

The Hydrodynamics of Planing Hulls
Allan B. Murray
SNAME Trans. 58:658-692; 1950
(SNAME is the Society of Naval Architects and Marine Engineers)

And the very useful:

How to Design Planing Hulls
subtitled: Basic principles underlying performance of successful high-speed V-bottom boats, and methods of applying these principles in the design of a modern planing hull
Jim Stoltz, Joseph G. Koelbel, Jr., and John D. Beinert
Volume 49 of the Ideal Motor Boating Series
1963

The latter is a lot more fun with how to scale and test with models, basic calculations, etc. Of more recent vintage and possibly easier to find.

Doug Wilde

[rbgarr]

'Improving performance by modifying the wake'? Sounds to me like the boats didn't perform as planned for.

I agree that the 'fuel drop tank' sounds like it may have been the genesis of the idea behind Elco's research. A later part of the chapter discusses methods of making fuel transfers at sea, describing 'fishing' for fuel. This method involves dropping strings of 55 gallon drums of fuel over the side of the mother ship to be picked up by the smaller craft(!) Couldn't have been 100% successful, I imagine.

I could see a lobsterman having a trailer on hand to help bring in all his traps when storms approach, though.

[Hazy Chris]

If you are going to go through the excercise of designing a "boat trailer", seems to me it would be silly not to make it look like an old "airstream" trailer on the outside above the water. I bet you could quadruple the double take factor. (which would already be pretty high) - My two cents. http://media5.hypernet.com/~dick/ubb/smile.gif

[HizzenanHern]

All of a sudden I'm thinking of a trailer hull flush with the water, with an inclosure the shape of a submarine sail, complete with periscope. That really ought to cause collateral boating accidents when towed astern as speed.