Building a hard dodger

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Building a hard dodger

Postby Michel » Wed Sep 16, 2009 2:58 pm

After the dodger designer got out of my project because of lack of time I got stuck with CAD files I could not work with. I already had taken the basic required dimensions off the deck and dodger. So I started to make a 1:10 scale mockup of a part of the deck of my F44 to get to grips with the aesthetics of a hard dodger. The mockup is made from frozen pizza boxes. I made different window configurations on white paper to see what looks best.

If you like to follow the project, have a look at http://picasaweb.google.nl/michcap5/HardDodgerProject#
Last edited by Michel on Thu Sep 17, 2009 5:02 pm, edited 1 time in total.
Michel Capel, Freedom 44 #4 1981 'Alabama Queen', NED8188, cat ketch with wishbones, home port Enkhuizen, the Netherlands, 52*42.238'N 005*18.154'E.
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Re: Building a hard dodger

Postby THATBOATGUY » Wed Sep 16, 2009 10:33 pm

Michel wrote:After the dodger designer got out of my project because of lack of time I got stock with CAD files I could not work with. I already had taken the basic required dimensions off the deck and dodger. So I started to make a 1:10 scale mockup of a part of the deck of my F44 to get to grips with the aesthetics of a hard dodger. The mockup is made from frozen pizza boxes. I made different window configurations on white paper to see what looks best.

If you like to follow the project, have a look at http://picasaweb.google.nl/michcap5/HardDodgerProject#


So the box on deck is a raft? I think the dodger looks great btw!

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Re: Building a hard dodger

Postby Michel » Thu Sep 17, 2009 2:19 am

The box is a raft; I admit it is a bit boxy, hard to make soft chines in cardboard. I put the raft on the mockup because it influences the window usage. On the dodger, the chines will be round. The front chine above the windows will get something in the area of 4" radius edge, the side edges will be around 1.5" to 2" radius. Still thinking how to show this in cardboard.
Last edited by Michel on Thu Sep 17, 2009 10:51 am, edited 1 time in total.
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Re: Building a hard dodger

Postby katorpus » Thu Sep 17, 2009 8:59 am

I have a couple of questions, Michel...

Will this dodger be constructed as a separate, removable "stand alone" attachment, or are you planning to glass it to the deck permanently?

Have you considered designing the forward windows essentially "pop-out" when relatively little pressure is applied from "inside" the dodger? I'm thinking of the stories I've read here & there where people have had their entire dodgers swept away when they get seriously "pooped" by a wave from the stern or stern quarter.

You might also give some thought to "damming up" the water that flows down the aft bulkhead along the edges of the coachroof inside the breakwater. You could build in a scupper hole just forward of this dam & drain it out on each side (through hoses inside the boat) into the channel around the lazarette cover/seat that it already drains to. Your coachroof won't cause more water to flow along this path than what would otherwise, but the airflow accompanying it will certainly increase in velocity and possibly create an unpleasant spray. A little woodwork could easily mask your interior plumbing.

This is a great looking design, by the way.
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Re: Building a hard dodger

Postby Michel » Thu Sep 17, 2009 11:09 am

katorpus wrote:I have a couple of questions, Michel...

Will this dodger be constructed as a separate, removable "stand alone" attachment, or are you planning to glass it to the deck permanently?

Have you considered designing the forward windows essentially "pop-out" when relatively little pressure is applied from "inside" the dodger? I'm thinking of the stories I've read here & there where people have had their entire dodgers swept away when they get seriously "pooped" by a wave from the stern or stern quarter.

You might also give some thought to "damming up" the water that flows down the aft bulkhead along the edges of the coachroof inside the breakwater. You could build in a scupper hole just forward of this dam & drain it out on each side (through hoses inside the boat) into the channel around the lazarette cover/seat that it already drains to. Your coachroof won't cause more water to flow along this path than what would otherwise, but the airflow accompanying it will certainly increase in velocity and possibly create an unpleasant spray. A little woodwork could easily mask your interior plumbing.

This is a great looking design, by the way.


John, thanks for your questions; they make me think through things better.

The dodger will be constructed in a female mold from epoxy, glass and foam. I'm thinking of 10 mm foam with a doubled up section at the aft edge of the dodger. Glass will be 600 grams/sq meter each side of the foam.

Q1) The dodger will be stand alone, with a 2" flangs in the inside, bolted through the deck. It can be removed, but you end up with holes or studs.
Q2) The windows will be pop out, glued into rebates. Preferably no screws, but that depends on my possibilities to bend the acrylic. I'm thinking of 1/4" - 6 mm clear window. The roof windows probably thicker; you have to be able to stand and fall on it.
Q3) Good thinking, but a dam and scupper hole in the breakwater are already present in the F44, I'll add a photo to the set. The scupper hole drains on deck. The dodger will sit inside the breakwater to allow water to run to the dam and hole, then further aft, there will be no flange and the dodger will sit flat against the inside of the coaming over the cockpit seats.

Any other ideas, questions, doubts etcetera are highly appreciated!

Questions to you guys:
- The roof will have a camber of 10% (20cm high over a length of 2 meters); will a foam core of 1 cm with say 3 mm laminate on both sides be strong enough to allow a person to fall on the dodger?
- Is 1/4" - 6mm acrylic or plexiglass thick enough to hold a wave jumping an board?
Last edited by Michel on Thu Sep 17, 2009 1:11 pm, edited 1 time in total.
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Re: Building a hard dodger

Postby katorpus » Thu Sep 17, 2009 12:02 pm

Sounds good to me. I'm going to have to bow to the greater knowledge of others on the question of strength, layup schedule etc.

One thing you might consider...given the relative permanency of your installation here...is leaving enough of a gap on the top/sides of the hatch turtle to be able to unscrew it and work it out of the "hole" in the event that you need to do maintenance/replacement of the sliding acrylic hatch and/or track. You could seal this gap with heavy foam cut to fit and plan on replacing it every now and then. You might even get a "custom cut" piece of coated closed cell foam from somebody like "C-Cushions" in Rockport, TX to use as a gasket. Good people, good products. (no financial connection here, I'm just a long-term satisfied customer...tell Bill Coxwell I sent you)

http://www.ccushions.com/
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Re: Building a hard dodger

Postby Michel » Thu Sep 17, 2009 1:31 pm

John, I planned a neoprene strip under the dodger flange all the way around; no 3M 5300 or similar glue. It might indeed be wise to leave a bigger gap above the hatch garage. I also have to think of permanently removing the two garage screws that happen to end up under the dodger. If not, I can't slide the garage aft.

Making the mold for the deck flange will be a challenge anyway; it has to follow all the ups and downs of deck and garage. I'm thinking of using a heat gun and (thermoplastic) PVC strip to make the mold for the flange. The front of the dodger will not have to be watertight; there have to be two slots to let the main and mizzen lines enter the cockpit.

Other questions:
1) the slots for the lines: how can I make them as watertight as possible?
2) ventilation: do I need it? We are at lattitude 52* (North of Newfoundland, to give you a pointer). I thought of putting an opening hatch in the middle window, but that will break the uniformity of the front. And I can't find simple hatches with clear glass, only smoke. If I could get a set of hatch hinges and a locking handle, I could use my own glass. Other ideas welcome.
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Re: Building a hard dodger

Postby katorpus » Thu Sep 17, 2009 4:16 pm

well...your most absolute water tightness would probably be fairlead ferrules for each line (sized to fit each line) cast into the leading edge of the dodger, but that would present problems of its own...
1) The path of the line (in tension) would need to be exquisitely fair from the breakwater back to the line stopper, lest you stress the dodger.
2) You'd have to make sure that you never let a line run free through the stopper, lest the bitter end whip up and take out a window. (Probably, this is true in any case.

You might consider building a covered "channel" between the breakwater & the dodger to contain the lines (upside down sprung "U" shape). You could mount a set of the fairlead ferrules ahead of the dodger (maybe halfway), incorporated into the support for the channel, which would "seal" the fore & aft halfs of the channel from each other. You could then mount the channel "proud" of the deck a little or provide weep holes (a la dorade box), and any water pumped into the channel through the holes in the breakwater should effectively be prevented from travelling all the way back to the dodger. This would have the added advantage of eliminating the "rolling" hazard of working on deck inside the breakwater (by not having lines on deck where you can step on them). I've long thought that this would be an elegant solution on the foredeck as well, as I they seem to always be underfoot when I go forward.

I'm unclear as to how much "bend" you are contemplating in your windows. It would likely be more pricey upfront (but maybe not in the long run) to have safety glass made to fit). Weight may also be an issue. You could likely get by just fine with the "side window" glass rather than the laminated "windshield" stuff. More susceptable to an errant winch handle (or heavy pointy things dropped from the masthead) than acrylic, but optically superior.

I wouldn't think that a hatch opening forward would be necessary in a dodger (it's not a sealed pilothouse, after all) in any latitude. The "station wagon effect" draws air into the companionway hatch and out the forward & midship hatches when the boat is in motion upwind. If the conditions are such that you have THAT hatch closed, chances are you won't be worried about ventilation. If you're worried about things getting hot up on your new "dashboard" while in a marina slip or at anchor, you might consider an external shade or awning to cover the forward windows.

I'd make the "top hatches" from stock hatches, and have them opening rather than fixed. Youl'll want them positioned so that you can see your sail trim from your "on watch" position under the dodger. Smoked lenses would be better here.
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Re: Building a hard dodger

Postby Michel » Thu Sep 17, 2009 4:57 pm

Smart thoughts about ventilation! Nice term, the station wagon effect. The roof windows I'd also like in clear glass, otherwise you don't see the sail and then I might as well leave these windows out. The problem with off-the-shelve hatches is that the rebate in the cambered roof is more complicated to make than with just a sheet of acrylic that can be bent in the same camber as the roof and therefore only requires an 'even' rebate. I think I can bend these window acrylics myself with a mold (a curved sheet of thin sheet metal) and a heat gun. The largest window is maybe 2 'x 2' so that must be possible with a heat gun or even in my kitchen oven. Having safety or tempered glass made is possible, but having it made in a curve is very expensive because they need to make a metal mold for the bending.

The ferrules present a problem wherever you place them; You can never change a line run or add a line. I was thinking of two rectangular openings (one for the mainsail lines, one for the mizzen lines) and cover the openings with a strip of UHMW plastic sheet with a hole for each line. The sheets screwed to the outside of the dodger over the openings. I found this solution in Steve Dashew's Encyclopedia. The tunnel idea to cover the lines is nice though.
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Re: Building a hard dodger

Postby THATBOATGUY » Thu Sep 17, 2009 10:31 pm

You could soften the pizza box cardboard chines with drinking straws. ;)

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