V12 Questions for Jacques

Boats up to 15' for oars, power or sail. Please include the boat type in your question.
Jeff
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V12 Questions for Jacques

Post by Jeff » Mon May 18, 2020 8:38 am

This question arrived via email over the weekend: "Hi, I just bought a set of plans for the V12 dinghy and wanted to check on a potential modification. I'd like to make the sides a little higher as my kids will feel more secure that way when they're in the boat. Would I be OK to add around 6-8" to the sides and transom and then scale up other parts appropriately? I'm building the boat for a small electric outboard only (or occasional rowing) and have no plans to ever put a sail on it. It's my second wooden boat so have a reasonable idea of the build process and would use the standard heights to establish the correct beam. Thanks," Jeff



GrantA
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Re: V12 Questions for Jacques

Post by GrantA » Tue May 19, 2020 6:42 am

Hi,
This was my question.

I had a search through the forums and it seems that I'm not alone in asking this one. Based on the responses it seems that I have about a 90% chance of being told that it's a bad idea! :D

So, in thinking of alternative solutions I was wondering whether installing handrails along the length of the boat would be a better solution. The goal is only for the perception of safety - I realise that the boat is perfectly safe as it is. I would likely make two for each side, leaving a gap for the oarlocks.

The perception of safety thing really is an issue for me. I built a small sailing skiff a few years ago with about 2" less freeboard than the V12 and the kids were not keen on being in it, even rowing. We then tried a small aluminium boat which had more freeboard and they were content with that (it had other problems though).

Thanks in advance!
Grant

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Re: V12 Questions for Jacques

Post by Jaysen » Tue May 19, 2020 7:28 am

I didn't answer originally as I am not the designer.

you CAN do it. Just remember that you are changing a lot of things.
1. The angle of oars to water... longer oars needed.
2. The min hight of the rower (or you need even LONGER oars)
3. The beam will be wider ABOVE THE WATER LINE which will actually make it a bit less stable on the "lean over"
4. You will need 3 more sheets of ply
5. you will need to GLASS that joint is it is not a chine if you don't make the sides full height. Lets talk about making the sides as "one wider piece"

That said...
the sides on the v12 are steeply angled and curved. So saying "i want 3" more freeboard" becomes a bit of a trigonometry exercise. Let's assume you do the math and need to actually add 5" to get the height you want. I would add that to the INITIAL cut out of the sides. This will most likely require more than 2 sheets to make a single side which will add another joint in the side. Trace rub rails at this point because they will be dang near impossible later (ask me how I know).

Once you have your sides cut, use crap lumber to make all internal frames EXCEPT transom. You have to make the transom with the extra hight right out of the gate, but it is the easy one as it is literally the exact length of the end of the side. Assemble per plan. You do not glue/glass the frames until the first flip IIRC. Once you have the bow, transom, and chines taped on exterior, flip (per instructions) and ONE AT A TIME make the real frames using the placement of existing frames to get measurements. Remember that the sides on v12 are very dependent on the frames for strength. Your longitudinal placement and height are important. Once you have your measurement, make the real frame, remove the garbage frame, tape the interior joint, install final frame, glue and tape it.

Hopefully JM will chime in and make any corrections needed.

Good luck.
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Re: V12 Questions for Jacques

Post by GrantA » Tue May 19, 2020 7:55 am

Thanks for the response (and for posting such complete information on your own V12 build which I read as a sort of study plan).

I'm not building a sailing version so looking at the plans and the nesting diagrams I worked out that I only needed 1 extra sheet of 6mm ply, and in fact while the BOM says 4 sheets of 4mm based on nesting drawings one of those must be for the sailing parts so if I build the standard one I only need three sheets of 6mm. I worked it out as the basic nesting diagram shows two sheet needed for one bottom panel and two sides, then only one more sheet for the other bottom panel. If I go with my height extension then each two sheets of ply gives me one complete bottom and one complete side.

One thing I hadn't realised was that the side frames need to go up to the top so this is where I think I might end up needing more ply as the two 9mm sheets are pretty tightly nested.

The rowing side isn't a problem as I would probably only be using these in the event of engine failure.

What I am concerned about (and with other background reading too) is how the higher sides are going to flare out more and, as you say, will make it a bit less stable when I'm leaning over to land all those fish I plan to catch. The handrail idea is getting more attractive by the minute as it could be angled straight up, and also wouldn't cause any rowing problems if I did decide to get a workout in on a fishing trip. (More likely I screw up on battery estimates!)

Decisions, decisions!

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Re: V12 Questions for Jacques

Post by Jaysen » Tue May 19, 2020 8:14 am

Bottoms and sides are both two pieces. The “extra” sailing parts are scrap from the standard nesting AND that nesting is pretty tight.

The other option you have it to make the extension another “chine” of sorts. This still requires longer frames/transom as well as glassing the joint in and out. Basically, make the sides to plan. Before assembly starts trace put the side top so you have a template. Extend that line 3” 90deg from the template line and extend the trailing end parallel to the side transom ends (keeps the transom as a single piece in one plane). I’d use the temp frames method still and assemble per plan. DO NOT PERM ATTACH THE TRANSOM YET. When you have the outside taped flip and start making final frames. Add the 3” vertical support to the frames. Stitch in the extra panel, tape exterior. Tape in frames. Tape interior.

Have you considered a FL? It might be closer to what you want with no changes.
Visit my official Class Globe 580 build blog at https://jaysenodell.com/globe-580
Currently starting a build of "Lil Bit More". A Class Mini 5.80
Class Mini 580 welcome post.
My already completed 'Lil Bit'. A Martens Goosen V12 set up to sail me to the fishing holes.
Jaysen wrote:
Mon Apr 29, 2019 3:44 pm
I tried to say something but God thought I was wrong and filled my mouth with saltwater. I kept my pie hole shut after that.

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Re: V12 Questions for Jacques

Post by jacquesmm » Tue May 19, 2020 2:04 pm

Very good replies by Jaysen, thank you.

All this is based on the assumption that the sides of the V12 are too low but why do you think so?
I designed her to be a dinghy to service a larger boat and as such, she had to be able to take a good load and handle safely in rough weather. She does all that.
Look at the pictures at BBC:
https://bateau.com/boats/V12/index.php#/8
and
https://bateau.com/boats/V12/index.php#/51

There are more than 50 pictures, many in the water loaded with crew.
The freeboard is normal, standard for a boat that size.

If you raise the sides, in addition to what Jaysen mentioned, you will also raise the CG and as such, the boat will be less stable. She will have more windage, that makes her less safe.
The beam at the oars will increase: you"ll need extra large oars, you will have to raise the seat.
All that will cost you 3 extra sheets of plywood and extra labor.

The V12 is a well proportioned boat but with a raised sheer, she will look weird. As Jaysen said, it can be done.

Build her as designed, launch her and test. If you feel that you need some kind of railing, add that but it will not be necessary.
Jacques Mertens - Designer
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Re: V12 Questions for Jacques

Post by terrulian » Wed May 20, 2020 10:32 am

Very interesting discussion. My much less detailed opinion is this: I think you'd be hard pressed to find a builder in this forum that found his JM designed boat unseaworthy or squirrelly. It's very unlikely that any of us have as much experience or knowledge of the fundamentals of boat design as Jacques. I wouldn't re-invent the wheel. I built a V10 which is a smaller version of the same boat that Jaysen built. I've always been a bit surprised at how well she handles in chop.
If you really want a tender that isn't at all tippy, you need an inflatable, preferably an RIB. Everything in sailing is a tradeoff and there is no perfect solution that does everything.
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Re: V12 Questions for Jacques

Post by Netpackrat » Thu May 21, 2020 12:51 am

Honestly it seems like you are looking for a hardware solution to what is strictly a software problem. Probably easier and better in the end to work on getting the kids used to being in a small boat. I have had both of my kids (7 and 4 at the time) and myself in a D5 with the sail rig, and while at under 8' it's definitely too small, they didn't seem scared at all.

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Re: V12 Questions for Jacques

Post by terrulian » Thu May 21, 2020 2:12 am

Honestly it seems like you are looking for a hardware solution to what is strictly a software problem. Probably easier and better in the end to work on getting the kids used to being in a small boat. I have had both of my kids (7 and 4 at the time) and myself in a D5 with the sail rig, and while at under 8' it's definitely too small, they didn't seem scared at all.
8)
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Re: V12 Questions for Jacques

Post by GrantA » Thu May 21, 2020 7:14 pm

I've come across what may or may not be a problem with the plans of my measuring. I've transferred the measurements for the mid-seat frame and I wanted to double check the lengths of each side to the lengths on the bottom and side panels.

The bottom panel at that point is 491mm and the corresponding length of the mid-seat frame is about that. However the side frame at that point is 409mm but that length as I've plotted it is only 370mm, so I'm 39mm short. I guess that some of the difference is due to the butt blocks but this seems like a little too much. I've also looked at other build diaries and one of them built from the CNC kits definitely has the panels going up to the top of the frame.

Help!

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