C19 Stretch and re-build - Launched!!

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TomTom
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Re: C19 Stretch and re-build Progress Report...

Post by TomTom »

OneWayTraffic wrote: Tue Nov 17, 2020 1:51 pm
Tolman skiffs have nearly an identical hull shape to the C series boats. About 45 deadrise at entry, 10 degrees at transom. Constant deadrise over the last half of the hull. I have the book, and it's a good read. Main difference to the C series is that the stern is not pinched at all. The C series have a slight pinch. Because of that they are often stretched. The C17 is almost identical to a widebody (except for the chine flats) and the C19 would probably be similar to a shorter jumbo.

The important point is that Tolman skiffs are often stretched to any arbitary length. It doesn't seem to affect the properties of them much.
They have a very loyal following for sure. Jacques does too and rightly so. But maybe anytime you get your hands dirty for hours/ years on end with a project that preoccupies your mind you are invariably going to be passionate about what you built.

I have read a few stories/ posts about the Tolman’s and some great trips by their owners. Amazing fuel economy report (by a David Nolan who built a Jumbo 27) when compared to factory built boats doing the same overnight trips out for tuna.

I can’t help but wonder how much of this is due to weight being so much lighter than any inherent quality of hull design?

I believe there was a David Gerr article that basically summed up boat efficiency down to 1) weight 2) longer and leaner 3) efficient power source and all else is minor detail.... (I may be misquoting though)!



I also have the Novi 23 plans - which I believe is a “Variable Deadrise” or “Warped Plane” design. To my untrained eye the difference is very subtle between that and the C series. Yet I believe the Novi and DE builders report almost no planing hump. I am very curious about this subtle distinction, how it is achieved and why it isn’t taken advantage of more often.

I wonder whether the Tolman’s have a noticeable planing hump given they are a constant deadrise?

I am also curious why Tolman chose the constant deadrise?

In any case, whatever was decided I guess it worked because people do seem to love them.

I am also curious as to how the designs are lengthened. Do builders increase the bottom thickness and glass or simply add extra frames?

I am hoping to find out soon enough how mine will perform!

cracked_ribs
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Re: C19 Stretch and re-build Progress Report...

Post by cracked_ribs »

I think the Gerr comment is pretty bang on...the Tolman is pretty similar to a C series. Relatively shallow deadrise, lightweight, not a ton of wetted surface, a little on the narrow side in some lengths, at least. That's a recipe for a low fuel bill.

If I had to guess, I'd say he went with a prismatic hull because it's easier to design, not to mention extend or expand. I think a warped plane needs to be tailored to its exact requirements more. I can knock off a prismatic hull bottom and feel pretty confident about what it will do. I wouldn't be confident about doing that with a warped plane.

I could be wrong but I think with a bit of weight forward on your boat and the extended hull, I don't think you'll see all that much bow rise either.
I designed my own boat. This is the build thread:

viewtopic.php?f=12&t=65349

OneWayTraffic
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Re: C19 Stretch and re-build Progress Report...

Post by OneWayTraffic »

Tolmans have a 12mm ply bottom. The ply is scarfed to length where needed. The front section is made from 2 layers of 6mm laminated. The ply is glassed both sides with 300gsm woven cloth and then there is some layers of woven tape at the keel and chines. There are two stringers only (ideally made from LVL) no frames. The sole is optional. The whole idea was to make a solid enough skin that the interior framing could be much reduced. Because there are no frames, the design is very modifiable. There's a Tolman forum on the net, where they talk about all those details.

The one thing I like is the thicker ply on the bottom. If I was doing my build over, I'd use 9mm ply over the back section of my boat, and 6mm on the front. In my build the 6mm ply sagged a bit between some frames, leading to a lot of fairing. Some of that was my own fault, as a long time went between planking and final glass.

Fuzz
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Re: C19 Stretch and re-build Progress Report...

Post by Fuzz »

The Tolmans were designed to give a good turn of speed and do so with low horse power. To do that they need to be kept light thus only two stringers and no framing. They worked and worked well but builders were not happy with the speed and started putting way more power on them than Renn had intended. The result was a number of them cracked the stringers. As they say you can't fix stupid. :help:

TomTom
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Re: C19 Stretch and re-build Progress Report...

Post by TomTom »

Fuzz wrote: Wed Nov 18, 2020 2:02 am The Tolmans were designed to give a good turn of speed and do so with low horse power. To do that they need to be kept light thus only two stringers and no framing. They worked and worked well but builders were not happy with the speed and started putting way more power on them than Renn had intended. The result was a number of them cracked the stringers. As they say you can't fix stupid. :help:
Would you say the C series is a stronger design? 4 stringers. Sole not optional but structural?

Then add foam filled as well generally?

I guess any boat can break but I can’t help but feel that a designer selling plans must have in the back of his mind the need to put in a huge margin of safety because of the Cavalier attitude to just sticking bigger and bigger motors on the back...

Was Tolman as constrained by this? Did he sell plans or a How to Book? Does that change your liability as a designer?

cracked_ribs
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Re: C19 Stretch and re-build Progress Report...

Post by cracked_ribs »

Personally, I think the C series is a stronger design; I have never attempted the math on either design but just looking over both, I prefer the smaller unsupported park size of the C boats. The thicker ply on the Tolmans is a necessity, I think, because of the single stringer per side. The unsupported areas are necessarily larger. Plus the soles on the C boats as I think you noted is not optional but structural - that box is very strong.

Liability issues I don't know anything about, I just build boats, write stuff and design communication systems.

I'm not anti-tolman at all (I don't own Tolman plans but I do own Great Alaskan plans and I'd consider building one, for sure) but I think the C series is a step up from the Tolmans as designs go.
I designed my own boat. This is the build thread:

viewtopic.php?f=12&t=65349

TomTom
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Re: C19 Stretch and re-build Progress Report...

Post by TomTom »

Curious if most people brush or roller in their lockers?

This time around I don’t think I have the stamina to worry too much about the finish inside lockers ... but I feel that a bit of texture probably helps conceal all the defects?

Fuzz
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Re: C19 Stretch and re-build Progress Report...

Post by Fuzz »

I don't think Renn was a trained navel engineer. He was just a pretty smart fellow who needed a boat to run around in that did not cost a ton to build or operate. He built a boat and it worked out so well others wanted one and the whole thing evolved. It is the wood in a tolman and not the glass that makes it strong. I know of one 26 footer being built that has two layers of 6 oz cloth on the outside. Not sure what the plan is for the inside as it was still upside down when I saw it.
In my mind the C series are much stiffer boats. They have more stringers and framing. But the Tolmans work and work well. I have seen a 20 foot Tolman with a cabin and three men in it push up on step with 40 hp. I was darn impressed.

OneWayTraffic
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Re: C19 Stretch and re-build Progress Report...

Post by OneWayTraffic »

If you deck a Tolman you could install all the frames. The larger boats have more stringers as well.

If you build a C series you can add glass or use 9mm ply.

But both boats are more than strong enough for the use so why bother.

I saw the main disadvantages of the Tolman the large amount of fitting from the boat (the side panels are not developed using CAD you need to plank scribe remove cut replank.) The use of imperial measures and the references to things I can’t get in NZ. It’s definitely a how to book with comprehensive notes. You can get a copy sent on Amazon for not that much $.

TomTom
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Re: C19 Stretch and re-build Progress Report...

Post by TomTom »

Final topcoat of Jotun Hardtop white on the outside....

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