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.
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.
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.
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?
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)
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:
the slots for the lines: how can I make them as watertight as possible?
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.
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…
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.
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.
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.
Hi Michel,
Nice to see your considered and thoughtful approach to the hard dodger. They make such a difference to your comfort and can really enhance the apperance of the ship if done well. On the other hand, there are many examples of poorly thouught out dodgers that just ruin the appearance of the ship. On my old Rasmus we did the dodger thing a couple of years ago. As I was short of time and bearing inmind the foregoing, I decided to get the professionals to do the job. The first and most important thing was to get the shape right. Two points were that the camber was the same as the cabin top and the angle of the forward window was paralell to the vang. The pros then constructed a mock up using 3 mm mdf and a glue gun and experimented with window sizes and shapes until they got the right look. This structure was then lifted off and used to fabricate a frame work around which the dodger could be built. it was constructed of 18mm ply with a 4 layer laminated roof. A couple of hanging knees to strengthen the aft section. Glass windows fitted with simpson construction adhesive with a uv primer on the glass. Safety glass by the way. 6mm if I remember correctly. This site should give you the pictures. http://www.trademe.co.nz/Trade-Me-Motors/Boats-marine/Yachts-sail-boats/Moored-boats/auction-241139474.htm Cost was NZD11,000 and I did the glazing.
Mike, nice piece of work on your Rasmus. Very special boat, a wooden Halberg Rassy. Looks like your dodger pros did the same thing as I did, only I start with cardboard. Your dodger was built from 18 mm ply, so it must have been quite heavy. I’m thinking of 10 mm PU or PVC foam and an outside laminate of 4 mm and an inside of 2 mm. But I must check if the roof will me strong enough. The sides with all the window rebates will be almost solid laminate with a lot of strength because of the rebate ridges.
Because I want to work with a female mold, it’s hard to test window configurations on the full scale model. The female mold will be put together on board and connected to the deck flange in situ. I’m now working on a more roundish dodger design bent from just two sheets, front and sides in one piece plus a roof. This one will also have rounded windows, so they will not be glass.
I would think that the oven approach is better than the heat gun approach. A heat gun doesn’t get a large area at a uniform temperature unless you are really incredibly good with it, and still wouldn’t be as even as an oven.
I recall a discussion of replacing the curved sliding companionway hatch which indicated that the method used was to heat the new plastic in some sort of oven, then take it out and lay it on top of the old hatch, using that as a mold.
The other option is to try and design for flat sections where the windows go. Should be very possible to do on the front, but would be hard to do on the top. This gives you a lot more options of glass / plastic, and makes replacement much easier and more flexible in case of accidents.
Sounds pretty reasonable, but I’m giving you a seat-of-the-pants opinion rather than a measured engineering opinion.
I’ve been working on my deck and I’ve got a core sample I took out. The factory laminate was ~5mm outside laminate and ~3mm inside laminate. The core was balsa, and it was ~13mm in the side decks, but ~20mm on the main cabin top.
The deck was still felt solid even in a section (almost 1m^2) that had the core pretty completely rotted away, so it is obviously very strong and stiff.
My only suggestion is that stiffness increases greatly with core thickness, so you might wish to increase that to 15~20mm from your original 10mm.
Let me also observe that I am gaining a new respect for balsa core, as I’m repairing and replacing bad spots in my deck. You gotta be careful to keep water out, but it is stiffer and stronger than foam, and does pretty well at keeping water migrations strictly vertical. These days I’m more amazed at how much is still intact than I am discouraged at the damage done by years of leaks. Just make sure that any holes in it go through both cores if you do make holes–Most of my worst problems came from self-tapping screws that didn’t go through the bottom skin.
Thanks for your observations. The thing about the heatgun and oven is true, I’m reading a lot on this subject now. A heatgun is only suitable to create a fold in lexan or plexi. So if I want to do the bending myself, I need to design the windows to fit in my oven.
About the laminate, our decks also have a structural role in keeping the boat in one piece and keeping the masts on without too much torque in the hull. The dodger laminate therefore can be a bit lighter than the hull or deck. It has no structural function. At the aft edge of the dodger I plan to use a foam core of 20 mm. in a 10 or 15 cm wide strip.
One important property of balsa core I’d like to add is it’s resistance to tearing. If you have a foam laminate, you can rip both glass/resin parts off each other when you push a crow bar into the foam. Try this with balsa and you don’t succeed because of the strength of the balsa fibers. Balsa also resists denting much better than foam; most foams are not very elastic.
I am into the second generation of design for my F44 hard dodger. This one has a one piece rounded front and sides with 35* slant at the front. The flat paneled design had 50* slant because the front sheet was a rectangle bent backwards over the 1:10 cambered deck. The rounded design was much harder to make, lots of clipping of cardboard. If you like, have a look at the progress at http://picasaweb.google.com/michcap5/HardDodgerProject# .
Smart comments are always welcome, technical advice also.
I like the “less upright” look of the greater slant! The absence of a “standard boom” with boom vang gives you a lot more flexibility than what I’d have in the same installation.
I also like the integral “dam” to drain the water that gets past the breakwater. That’s obviously something that they “left out” on the F40 deck mold, and it would be a wooly-bear to try to incorporate now. I’m thinking my best bet for a retro-fit would be to glass in a lateral “handhold” at the outer ends of the bulkhead and cut a scupper hole in the “rain channel” forward of that, draining it through an internally-plumbed hole and out into the drainage channel at the hinge-side of the lazarette tops. The aft end of that channel (at the bulkhead) is higher than the channel just forward of it, resulting in a “bowl” that holds water until it evaporates (at the dock) and does not self-rinse the accumulated dirt (ever). This drives me crazy…that…along with the mis-placed side deck scuppers (not at the “low point” of the deck in normal dockside trim), which results in the same kind of dirt & puddle directly in front of the port side lifeline gate…nevermind that the starboard scupper drains down the hull directly above the opening port at the nav desk. Really great planning there!
I know what you mean about drainage. The first set of F44s (I have hull #4) have a 3’ gutter along the outer edge of the deck with a drain hole at the front of the gutter. Now I have a Northern Lights 6Kw generator mounted inside the transom, so imagine where my deckwater drains? Right, it doesn’t. Only if I fill the 175 gallon watertank under the V-berth will the water run out of the gutter. Otherwise, it sits there, with the dirt in it, right at the lifeline gates. On later F44s they left out the gutter and put a drain in the deck edge a bit more aft. Still not ideal, but better. I never understood Freedom’s ideas about getting water that is outside on the deck into the boat just to get it outside again via a series of Murphy-prone hoses, elbows and clamps. The UK F35 catketch also has an internal deck drain. Really bizarre.
Must be the UK built F-33/35 that has the internally run drains. On my US built F33 There are only the cutouts in the teack toerail and the transom drain for the cockpit. Unless F33s with aluminum toerails have a different drainage system.
I believe the previous owner cut some additional openings in the teak toerail to assist drainage so drainage design by Freedom must have been lacking in general.
I just saw an ad in the back of Soundings. It seems that Webasto is now making a “marine sunroof system”. Automotive style (opening) sunroof, available for OEM or retrofit in 7 sizes. Sounds expensive, but maybe worth a look
