Plank on Frame vs. Plywood on Jig

[Lowcountryboy]

What is the difference, performance wise, between Plank on Frame verses Plywood on Jig?

[billschwabe]

Hoo boy, This one is surely going to get a lot of hits, look out WorldCat this could surpass your record! I guess I'll start the ball, and the holwing, rolling.

IMHO (and a lot of naval architects as well) cold molded is far superior in strength and durability than plank on frame especially if it is used on a boat destined to go fast. That is NOT to say plank on frame isn't good, there are a ton of boats out there doing just fine built that way. I ran a charterboat for ten years that is now 49 years old and still going strong but it wasn't a speed demon like todays battlewagons either.

Well built plank on frame boats usually don't have problems IF run with common sense at speeds up to about 30 knots. Above that, well-built cold-molded boats have shown themselves to be better at handling the stresses and pounding they have to endure over time. That's not to say that cold-molded is the end-all either, but up to about 40 knot cruise speeds, they seem to hold up just fine. My personal belief is that above 40, even cold-molded isn't going to be enough and composites have to be introduced into the equation but since there aren't many out there that cruise that fast yet, it remains to be seen.

Plank on frame can be built tough enough to handle those speeds but you get into triple framing on very close centers, skinning with plywood, and adding so much glasss you start getting heavier and more expensive than a cold-molded hull of the same strength.

A big factor is the design of the hull with either method. If the builder knows what the client wants to use for power and expects in speed, he can make adjustments. All too often I've seen older boats (mostly plank on frame but some cold molded as well), repowered with bigger engines than the builder designed for and it results in broken frames, torn out stringers and in extreme cases, sinkings.

Ok guys, I've got my kevlar flak jacket on, let er rip!

[Expeditor]

Sent you a PM, hope it helps...

[Sportsman 45]

What is the difference, performance wise, between Plank on Frame verses Plywood on Jig?

They both ride well, but the plank on frame is strong as it gets.

I've owned and fished both.

[Fortunate One]

How about plank on frame covered by a layer of bi-directional Okoume plywood and glass?

As far as performance, that has to be more deified.

Are we talking lightweight and speed or something that can blast through the waves and not give up much momentum?

A lot of people are under the impression that lighter is better.

Perhaps it is if you fish in a mill pond. I'm from the other camp. There's something to be said for weight combined with strength.

As someone told me a while ago "There ain't no replacement for displacement".

[tabasco]

you can cover your planks with whatever you like if its plank on frame it still depends on the frames and spacing/thickness for the strength? its a totally differently concept. A true cold molded boat has strength from the hull itself not the frames or the bulkheads. Monocoque or something like that. A framed boats' strength is the frames itself. I can cover a woven roving boat with okoume but how does that help? But then again I dont' understand moving away from cold molding and throwing multiple layers of super heavy cloth on top of multiple directional plywood planking???? is it a cold molded boat or a fiberglass boat with plywood coring?? Please educate me. Hopefully we can get someone to chime in on this one.

[billschwabe]

A lot of people are under the impression that lighter is better.

Perhaps it is if you fish in a mill pond. I'm from the other camp. There's something to be said for weight combined with strength

The old "heavier rides better" line, still tickles me when I hear it. Sure, at displacement and slow speeds, it may be true but NOT at planing speeds! Sure, the old venerable 54 Berties used to smash their way through just about anything but it wasn't exactly "smooth" when it got bad either, and you had to hang on every time you punched through one. I remember fishing on a 54 duiring a Big Rock 20+ years ago beating our way to the southwest into close together 6-8 footers and a Jim Smith blew by us (and the whole fleet!) at twice our speed. They were close enough I could see they were sitting comfortably on the bridge and even got the golf wave as they went by. You could see they weren't smashing their way through the waves like we were, they were slicing across just the tops because they weren't so heavy (and slow) they dropped into the troughs.

The biggest touters of heavy is good used to be Bertram and Hatteras but guess what, now they are bragging about "lightweight cores and sophisticated bottom designs that give better economy and ride". All of the major production builders are coring decks, cabins and hull sides now, coincidence? No, they got tired of all the custom boats blowing by them every day and burning half the fuel while doing it. Fish any tournament nowadays, which boats are the first ones out there and the first ones home? Not the heavy ones, they are the last ones at the dock and while they're pumping huge amounts of fuel for the next day, they always say, "well my ride was better", all the while glaring at the fast boats who are already cleaned up, sipping cocktails and getting ready to head to the tent for dinner.

[billschwabe]

A true cold molded boat has strength from the hull itself not the frames or the bulkheads

Exactly! Cold molded hulls are designed to flex to absorb impacts from wave slamming, not to a point it overstresses the hull, but flex some nonetheless. If you design for it and keep the flex within the limits of the structure, it will last. If you try to stiffen it up though, it will break and that's happened on a lot of early cold molded boats and probably given them a bad name. If you build a hull designed to flex, you can't create "hard points" and put in hard bulkheads, egg crating, or frames or you transmit that flex into the rest of the boat, usually breaking things. Combining frames with a cold molded shell is pitting one against the other and the frames will break every time because they don't flex.

A well designed plywood cold molded boat only relies on the glass skin to keep the water out and debris impacts from puncturing the hull and it takes suprisingly little glass (or even better, Kevlar) to do the job. Cold molding with a foam core however is a different matter as the foam's strength is nowhere near plywood, then you have to use thicker glass (or plywood) skins to get your panel strength.

[clt_capt]

Wow - a pretty loaded topic... But for a combination of strength, and weight, I'd have to say that cold molded is probably on top - the biaxial layers of plywood and the epoxy skins have a great strength to weight ratio...

[brokensheer]

I enjoy this great reading!, , I once had an internal battle with archery tackle, at the time every thing was going light and fast!, so like the crowd back then so did I.
Soon I had a shot at near 8 yards, I placed my easton super light and 100grain broad head right in the pumper!,, , the deer eased off as though nothing happend , I could see the wonderful blood trail as he stepped away, I sat for 45 min. and began to track him,,, nothing, the next day , nothing,, sick over loosing an animal, I went back to heavy arrow, , I found the skull the next season ,, and am still sick about it,,my thought if a hat pin blasted through me at the speed of sound, I will not feel it, but if a semi truck loaded with cast iron hits me ,, well its all over!,,