What to build?

The dead flat bottom seems more likely to have an improved ride, but I wonder what down-sea handling would be like ? My gut feeling is it would have to dig in and/or broach more than the "Digger" type. Maybe a lot of flare in the topsides would improve that.

 

Gardner's boat has lots of flare ...more than a Banks Dory. The bow is raked more than PAR's Digger. It's 14' OA and the bottom is 40" wide. It has 5' long skegs that are 5" tall at the aft end. On the face of a wave a dethrottled OB should help directional stability considerably. I would think a boat would turn better w some rocker. But a man that built the Flat Iron says it handles very well. But he was the guy that said it diddn't pound so ????

 

Those skegs are clearly to offset the tendency described. The dory style hull is appealing because of the 'instant boat' ease of building and economy of materials, but it is certainly not ideal shape wise. Depending on the intended usage, no doubt has a place.

 

Alright, if the "Flat Iron" pounds less, how about hooking the bottom down at the bow to pound even less ! A bit more depth to those skegs to counter the added lateral plane forward, even add a way for an air inlet to break the "suction" from under the bow with that negative angle of attack, and off we go !

 

Mr Efficiency, the name Digger is from its roots, which is a that of a clam digging skiff, used for about 100 years now, in most shoal areas in this country, I suspect around the world.

Tom you're right the bow has to be kept down and also fine if you expect to go out in anything but a calm. The boat should also have a fairly narrow beam/length ratio and "tuck in" just a little more then usual in plan view.

I agree that Graham's Marissa is a great design, though it's considerably more complex a build then Digger, even with Graham's innovative build method. I've just placed a bid on a Marissa build and likely will begin one this spring or early summer. I'm looking forward to it. I disagree with Easy Rider's assessment of Marissa, but you and I have considerably more insight to this particular design then most. I'll also be starting a LapWing soon, FYI.

Easy, Gardner's clam skiff has some of the features I previously stated, but not all and it does pound some, but not as badly as a poor flat bottom design, though it's size makes smoothing it out fairly easy with boat trim. This is a trait all flat bottom skippers learn.

This wouldn't be the case and wasn't when Gardner designed the boat. His interest was a clamming skiff of very simple arrangement. His rendition will not be as maneuverable as mine and it does have rocker, but on an outboard equipped boat, this is a relative term. I'm talking about his 15' 8" clam skiff (1982), which was an improvement of his 14' 4" clam skiff which he designed in the late 1940's.

This also wouldn't be the case. Outboard equipped boats don't get squishy in normal maneuvers or following seas, unless you've throttled way back to a point where the sea can have it's way with you or the exact opposite, you're going way to fast for the hull form, sea state or both.

As for the "ax bow" suggestion, well if you've never had a powerboat "root around" on you, well I recommend you put an ax bow on what ever you like. You'll remove it soon after it's found a contrary wave, but the lesson will be rewarding.

Flat bottom hull forms are the most efficient of the usual choices for a full plane shape. It has it's good and bad points, like all things. I'm just trying to break the common myths about them. Again, most are too wide for their length and many have too much beam in the forward sections. Also and which seems a mostly American issue, they get over powered, which tends to drive them into speeds they just aren't well suited to operate at.

I used to own a boat very similar to Digger, many years ago. It had developed a hook from years on a trailer and I got it when the owner found out how much it was to fix the hook. I made it a single step, flat bottom that would truly scoot. It would scare the crap out of most in it, which was enjoyable, but it proved even the lowly flat bottom was a mark to be reckoned with. I use to crush V bottoms with the same size engine. They all accused me of having a "hot" motor, but I was always happy to pop the cover and show them a bone stock 40 HP Mercury. I got a fair bit of free beer this way.

Lastly, I wouldn't burden a small powerboat with skegs of any kind, unless a straight shaft setup. They aren't necessary and are a throw back to days when you actually needed them. Digger has bottom runners to protect the hull in beachings, etc. but they don't need to be there for directional stability. In fact, she'd be more maneuverable without them. How many production boats, flat, V or round bottom with an I/O, jet or outboard do you see with a substantial skeg?

 

So the skegs Easy Rider says are on that boat ( "Flat Iron " ) are there for what purpose, would you say ?

 

There are a number of "Flat Irons" and honestly, I'm not sure which he means. Chapelle wrote about Flat irons (as one word), Jim Michalak, Reuel Parker, Phil Bolger, John Gardner, Bob Baker, Eric McNicholl, oh hell everyone has a flat iron design, pick someone.

Large skegs, like those seen on the Michalak designs are lateral area for sailing and really are useless drag on a small powerboat. If the boat is setup to row, then it could use a small skeg to help directional tracking, but a good design for rowing would be limited to displacement speeds under power. Skiffs designed to fully plane off, don't need them.

 

Absolutely. The only reason to have a bottom appendage on a small outboard powered boat is if it wants to slide in turns. On runabouts, I use a skid fin at about 30 to 40% forward of the wetted length and on more utilitarian boats I use a longer, but small, keel that stops abut 14" forward of the transom. Someone a while back mentioned putting twin skegs on an outboard to avoid ventilation in turns. That is opposite of good practice and will only enhance ventilation. Cruising boats need more directional stability and should have a deeper keel than small boats that don't need to hold a compass course.

Ignorance is not a sin for it can be cured by learning. Knowing stuff that ain't true is a sin.

 

The Flat Iron I speak of is in the back of the book called "The Dory Book" by John Gardner. I did some reading last night and found the bit about the skegs.
"Under no condition should the twin skegs, shown on the original boat as ending just forward of the motor well opening, be omitted". He says that in the text about a 19.6' skiff (semi-dory) 4' wide on the bottom. The same skegs are in the flat iron drawings. Apparently he thought the boat would handle like a greased plate without them. In my opinion the Flat Iron should handle about the same as the same boat w some rocker fwd as the fwd end is out of the water while planing. Ed Schock designed a series of sail boats that were basically flat bottomed boats that have 5 or 6 degrees of deadrise but look like a basic flat bottomed boat but has a slight V with constant deadrise over it's length. Seems it should turn better than the flat bottom especially if the boat is beamy. But since the chines, keel and stem meet just like a flat bottomed boat is should be very easy to build and perhaps an excellent boat for Potomac1. Did Schock design OB skiffs w this slightly V bottom form? If not who did?

 

PAR.. gotta say it, digger looks pretty sweet and efficient

 

Sounds like things can get ugly without the skegs, doesn't it, sure you lose with more drag and turning circle, but broaching is just no fun at all.

 

Look the jury has long since been in on this and it's not a debate, you either understand the affects of skegs or you don't. Gardener used skegs on his dory because it would "tuck it's tail" with too narrow of bearing area and too much "tuck" in plan view. This has been an issue with power dories for generations, which is why the type has been changed to the modified dory, which has a wider bottom panel (more bearing area) and much less aft tuck, so it doesn't want to hunch down in a turn.

 

PAR,
Haven't heard the expression "tuck". Is that where the beam decreases as you approach the stern? And at the chine I suppose. And if this is a debate what's it about?

 

Yes, the tuck in plan view is the decrease in beam, at the after end of the boat and in profile the amount of buttock angle. The two are distinctly different, as you can have one without the other, but the general approaches to both are well established. As a rule, you want no tuck in the buttocks of planning hulls and if there is tuck, no more then a few degrees is acceptable before you've created so much suction, that the boat will never plane. The only time you might want tuck in a planning hull, is to address low speed maneuverability, such as Gardner did on his flats skiffs, which also needed to be poled and occasional rowed. This trait by his own admission, limited speeds to a fair degree and initially caused concerns about porpoising, which was solved with a CG shift. Tuck in plan view permits the boat to turn better and "carve" when asked to turn, rather then skid or dig it's chine, which can "trip" her. Gardner's 15' 8" clam skiff has no such tuck, which makes it slightly less maneuverable, though her topside flare does mitigate any tripping tendency. Everything is a trade in yacht design, a decreased percentage of one, for an increased percentage of another feature. Life is much like this too.

 

As I contemplate Digger her simplicity becomes a bit like magic. She draws me in. I can hardly not start building.

PAR,
Could one build her w a double planked yellow cedar bottom and red cedar sides? If we increased her BLR a lot and increased her depth a bit would that ruin her manners or make her unsafe in any way? Almost all the skiffs on our bay are tinnies (Lunds) and I'd like to show that a good boat could be made from local materials. Would narrower make her more likely to trip on her chines? Would more flare mess w the simple build?