C17 - questions pre-build

[OlivierP]

Hi all

I have purchased the plans for the C17, which I intend to build as an open fishing boat, as it looks to be the best compromise for my use and waters. It will likely be close to the one built by Rmarsh which was my main inspiration. Center console with seat at the front, a pilot bench/leaning post, gunwales, casting deck, 50hp 4 stroke, 50l plastic tank above deck in the console, that's about it. The steering position will remain where drawn for the cabin version, and I'll keep the frames where designed.

I have redone the nesting to adjust to the absence of cabin, to my console/bench plans, and to the slightly larger length of plywood here : 250cm instead of 244. It should all fit in 20 planks - fingers crossed.

Based on my calculations and inventory, the expected empty boat weight with engine, all deck and safety equipment and full tank, will be between 550 and 600kg without crew, so approaching 700kg with just me, a cooler and my fishing gear (not counting the fish ), which is just the designed displacement at DWL with top of sole at the water level. As I want some margin and stay self bailing, ideally with a crew of 2-3, I'll raise the stringers and deck between 1 and 2'' - still thinking and calculating. There's plenty of freeboard anyway, and the VCG is lower with the absence of cabin.

Some preliminary questions after studying the plans, for BBC or anyone with knowledge of the boat :

- Bow mold: I only have the full size pdf in the plans (and cannot print full size), could BBC or anyone provide the drawing dimensions?
- What is the dimension of the overlap between the upper and lower side panels?
- The 6mm (1/4’’) marine plywood that I can find here always has 3 plys. I see sometimes 5 plys recommended for 6mm marine ply but can’t find any. The minimal 5 plys thickness I can find is 8mm, but I guess this is way too much an no substitute for 6mm. No issue building with 3 plys ?
- Long panels are assembled with 1 layer of biax tape each side of the joint (and putty inside the joint). Correct?
- Should one cut a 6mm offset in the frames at the transition between the lower and upper panel? Not drawn on the plans. Or simply fill the upper gap with epoxy ? I'm trying to save on epoxy.

There will be more questions I'm sure. Thanks in advance, when I move to the building stage I'll start a new thread in the Builders forum.

Cheers
Olivier from France

[jacquesmm]

From the designer, replies between the quotes:

Hi all

I have purchased the plans for the C17,
Some preliminary questions after studying the plans, for BBC or anyone with knowledge of the boat :

- Bow mold: I only have the full size pdf in the plans (and cannot print full size), could BBC or anyone provide the drawing dimensions?

The bow mold function is to keep the side panels from pulling forward producing an ugly dip in the sheer line at the bow. It does not have to be accurate but will allow you to stitch the sides to something and produce a nice sheer. I will post a simple drawing in the next post.

- What is the dimension of the overlap between the upper and lower side panels?

You don't need that dimension. If I give it, it may conflict with other measurements. If you follow my building sequence, the panels will overlap without measuring anything. Draw and cut the panels. Install the chine panel on the jig, one edge matching the bottom or following the chine corner points. Drop the sheer side panel on it and line that one up with the sheer edge on the frames. That's all there is to it. Do not measure the overlap, the sheer edge may move to the wrong place.

- The 6mm (1/4’’) marine plywood that I can find here always has 3 plys. I see sometimes 5 plys recommended for 6mm marine ply but can’t find any. The minimal 5 plys thickness I can find is 8mm, but I guess this is way too much an no substitute for 6mm. No issue building with 3 plys ?

Try to find quality ply, 6mm with 5 plies. If not, years ago, there was in France a type of exterior plywood with 5 plies in 8 mm. That one will require a little more work to bend at the bow but should be fine if there are no voids.

- Long panels are assembled with 1 layer of biax tape each side of the joint (and putty inside the joint). Correct?

Correct.

- Should one cut a 6mm offset in the frames at the transition between the lower and upper panel? Not drawn on the plans. Or simply fill the upper gap with epoxy ? I'm trying to save on epoxy.

Some builders do that, we never did on the prototypes and instead filled the gap with epoxy putty. In any case, you must fill that gap with epoxy but you save a little bit of putty with an offset. I would not do it.

Drawing in next post.

[jacquesmm]

Here is the bow mold.
Sorry, I only have the imperial one but it is easy to translate.
Click on the link and/or download.

https://www.community.boatbuildercentra ... ?pid=75561

It fits only one way, against the first mold. It does not have to be accurate. I like to shave about 1 cm of the front, it makes it easier to stitch the panels.

[OlivierP]

Perfect, thank you.

Yes I can find 8mm with 5 plies. It will be slightly heavier but so be it if it has the needed strength.

[OneWayTraffic]

I'll add a little to the overlap. It changes a bit depending on exactly how accurately you have cut the panels and stitched the boat. The dimensions of it hardly matter but are roughly 150mm. I lined up my side panels at the bow and stern and tried to get a good look. After flipping the boat I found that I would have benefited from a bow mold. In the end I accepted it and glued and filleted the backing block for the bow on the top of the bow rather than underneath. This somewhat hides the dip at the bow.

Also I would not bother raising the sole unless you leave it at a dock for extended periods. The boat should self drain at the dock empty, but a little extra margin would not hurt. If you are launching the boat from a trailer every use, there are many ways to dewater it. Scuppers with tubes, pumps or plugs in holes. The sheer height on mine is perfect as is for this 178cm tall man.

[Dan_Smullen]

Congratulations on commencement of the journey!

Good answers to your questions. All that I have to add is that I added 6mm strips between the back edge of the upper panels and the transom which filled the gap without using as much epoxy. After all is said and almost done, I have thought on a number of occasions that no continuous filler here would have been fine, maybe even aesthetically preferable. Any cavity needs to be filled, something of a wedge shape rather than parallel will be fine. Make sense?

X2 on raising the sole. It is good insurance against potentially building a boat the rides too low. No easy fix for that should you get too heavy and find yourself with wet feet.

Although not necessary, joints in the side panels landing on a frame would have afforded some additional comfort on my C19.

Best of luck getting started!

[Rmarsh]

Good choice by you to build the C17. I couldnt be happier with my C17 built as a center console.
I wouldnt raise the sole...just fine as designed. And no on notching the frames at the overlap....waste of time IMO.
Thirteen gal tank will be good ....i put a 19 and its overkill for all the trips ive made.
Good luck with your build.
Bob

[OlivierP]

Many thanks to all for your contributions, very helpful.

I'm still debating the sole level but my goal is to keep scuppers open as much as possible, both underway and at rest, with 2p on board. I want to rinse the deck with buckets of water flowing out to sea, and don't want to fish with wet feet. Besides, I have to cross a pretty rough inlet (the entrance of Golfe du Morbihan for those who know) with currents up to 8 knots, with wind against current the chop can become steep and nasty, it's easy to get quite some water in the cockpit so open scuppers are a major safety feature. I hope the high sides will help.

Out of curiosity, did anyone weigh a completed C17, or have any real world estimate of its final weight ? I don't see how I can get the empty boat ready to roll under 550kg (>1200lbs).

[jacquesmm]

About the self bailing cockpit: it is matter of boat size. In a small boat, you must compromise or select a larger boat. If you want a self bailing cockpit, you must raise the sole as you describe but, while doing that, you also raise the CG and make the cockpit shallower which is less safe. You should have the gunwale board above or at the knee cap. A lower gunwale may trip you.
In boats the size of the C17, the best compromise is what I show: a cockpit sole level sufficient to drain at the dock (rain) and with a light load of 2 persons.
Even with water over the sole, the C17 should not flood and be perfectly safe thanks to buoyancy foam.
It's my preference but you can raise the sole if you prefer.

I know the Morbihan. I had a friend that owned a bar restaurant in Larmor Baden. He had a couple of boats and we sailed often in the golfe. In good weather, it is one of the most beautiful sailing spots that I know. The pass can be rough.

[OneWayTraffic]

Have a look at my C17. Two very big scuppers out the back. They will have elephant trunk scuppers on them. If the boat is moving forward it will drain. At rest with people on board is another matter; you will get wet feet. That might not bother you though. There is also this amazing invention known as the 'plug.'

Scuppers open while crossing the bar, and closed while fishing.