Is this a box keel? Is it common?

[Commissioner]

I'd love to get some input on this hullform as I have not seen it before (Yes, I live a sheltered life). Vessel is a 25' plywood pilothouse fishing boat with a 60hp diesel that is installed deep into the keel thus allowing the engine to be entirely below decks in the open cockpit. Water & fuel is also carried in the fat "keel". With a dry weight of approx. 4500 lbs she apparently cruises at about 11 knots@1.25 gph. I'm curious to know if this hull would likely respond to perhaps 100hp to provide a 14-15 knot cruise? Thanks for your observations.



Exposed wood on the bottom of the keel is an oak skid plate (for beaching) which is attached over the glass/epoxy bottom. The fuzzy looking thing in the photo is a piece of carpet on the trailer support beam.



A view of the chine and the wide point in the keel



View aft with rudder on edge

[Mark Van]

It looks like a Seabright Skiff to me.

[JimD]

What do I know for sure but I think it's commonly called a seabright hull form, the history of which I don't know but I bet other forum members will. Just to toss in a couple examples from the Atkin website:

Atkin Seabright Skiff:

A Speedy Seabright Skiff While not a true Seabright skiff. Sun Ray is a development of the Jersey skiff which has considerable merit. The form as shown in the plans is very much like the newer craft built along the coast for fishing and other purposes; but rather than the more usual lap strake planking she is carvel planked. Then too, the box deadwood is a little different from the typical skiff. The change here is necessary for constructional purposes because smooth planking is used. These boats seem to have a very definite use, and at speeds up to 15 to 18 miles an hour are quite satisfactory. However, for high speed and for use in rough water a wholesome boat of the V bottom type is a far better craft. The one advantage the Seabright skiff has is its ability to land anywhere, through surf or in still water, and the fact that it can be beached without damaging the propeller or shaft. It will also stand on an even keel when on the bottom, or while being rolled up on rollers or skids. In choppy water the flat of the bottom slaps some and unless these boats are built moderately light they will pound and slap a great deal. One advantage a boat of this design has is that the motor can be set very nearly level, which is something worth having. A motor always will give better service if its crank shaft is level; not only does the lubricating system function more perfectly under this condition but the inflow of the gases is more uniform to all cylinders, and therefore the combustion is better; which of course will result in more economical operation.

And the sailboat Heart's Desire:

the excellent underwater form of the Sea Bright skiff

Ye that build Heart's Desire II can thank the Sea Bright skiff keel for these ample walking areas

True box keel designs I have seen look like real boxes, very square in cross section, built onto the bottom of the boat, quite narrow and foil shaped. In other words they look more like normal keels only hollow so they can be filled with ballast inside and thereby avoid having to hang ballast from the outside.

[Tom Robb]

It's a displacement hull. Speed is a function of LWL. Nearly doubling the HP may double the fuel consumption but she'd just squat with her bow in the air, making bigger hole in the water, and handle badly without going much faster.

[mmd]

What Tom said above. She's got a wide flat keel so that she can be beached with the tide and will stand on her own with only the most minimal of bracing until the next tide lifts her free again. I can't see if there is a monster eye in her bow, but if there is, she's made to be "drug up" on a beach or skidway.

[Donn]

Here's a bird's eye view of the box in the bottom of a sea Bright Skiff:

[Commissioner]

Gentlemen, thank you for the excellent input. As a neophyte I assumed that the chines and the flat keel bottom would provide some lift if the boat was pushed harder.

[nedL]

The simple answer to your question is "Yes" you could call that a variation of a boxed garboard keel. If you want to get a bit more specific, it would really be considered a deveopment of a "rolled garboard keel". Both 'boxed garboard' and ' rolled garboard keel construction was used in what people refer to as Sea Bright skiffs. (Gag, I don't like that incredibly generic, made up term. Oh well.) As has been pointed out, great for regular beaching.
In this specific situation I don't think that adding extra horsepower would be a good thing. Due to the significant deadrise along the entire bottom and lack of flat lifting surfaces she might get real squirly if pushed beyond hull speed. This is not the norm for rolled or boxed garboard keel Jersey skiffs. As far back as the 1930's builders such as Banfield and King were building stock lapstrake skiffs with boxed garboard keels that would do close to 30 knots. Charles Hankins' boats (the last builder of boxed garboard keel Jersey skiffs & the builder of the hull that Donn posted pics of) were quite able. His 24' shelter shelter cabin cruiser (w/ a true boxed garboard keel) would cruise comfortably at 12 knots, and would do 17 knots wide open, with an 80 hp 4 cyl Lehman Ford diesel.

[Commissioner]

Ned,

Thanks for your response.

In a discussion just today the owner revealed that when the boat was new the hull would lift to the point that it would raise the chine areas of the hull higher than the waterline and the boat would lean over as a result. The owner then added about 500 lbs of lead to force the boat back down into the water while underway and he was satisfied with the results.

I found that to be a remarkable bit of news. He went on to say that the designer commented at the time that more power may require the addition of even more lead. I looked in the hatches and sure enough, there are lead ingots distributed around below decks.

What do you make of this? Where would that lift be coming from with such modest power? The substantial flat keel bottom?

[Joe ( Cold Spring on Hudson )]

Coming along good Donn, launching this weekend ?

[JimD]

Coming along good Donn, launching this weekend ?

And things don't come along 'good', they along 'well'.

[nedL]

Yes, and that's pretty much what I meant by 'squirly', in that she will ride up on her plank keel, resulting in a significantly reduced waterline beam which will make her flop side to side.


Here you can see a true 'boxed garboard' keel, where the 'sides' of the boxed keel are not actually the garboard planks, but almost more like I guess you'd say 'stealer planks' on edge. They are triangular in shape and taper to nothing at the forward end of the box.

This shows the forward end of the boxed keel, where it tapers off. (There is a full length skeg below the boxed keel which may make the piicture cunfusing.)

If you look at the picture that Donn posted of his Hankins skiff, and this second view (also of his skiff) you can see that it is actually the garboard plank which makes up the 'box' of her keel, I believe really making this a rolled garboard keel.


Here is a 24' Hankins boxed garboard keel skiff doing about 12 knots.