Blackrock 24 (Build)

I very much appreciate your blog and am learning from it.

When you have advice from PAR and SS there is nothing useful I can add, so though following this with interest would not normally post.

Over 7600 views shows healthy interest.

 

LS, Thanks for the kinds words.

SS, I'll have to check out the "nuked" honey.

I did the torch trick (plumbers torch) with the last couple of roll on coats. The poppage was instant when the flame got near. I tried the blow dryer trick with dismal results. The "extra" blow dryer of my wife's couldn't blow dry a crew cut so I think it's an equipment problem. I did have some mild trepidation at putting an open flame to my boat. A task best done at the end of a boat's life, not at the beginning. I think I did on occasion get a whiff of burning epoxy, but no permanent scars were left. I see what you mean when you say, "You'll do it a lot", Paul. I went over almost every inch of the hull with that little flame. I think a fan type burner attachment would spread the flame and make the process go faster. I believe that It also helped the epoxy flow out as it's the best rolled epoxy I've done. It's not finish quality by any standard, but I see some potential. I'm thinking that a high powered hair dryer (or careful use of a heat gun) could get some localized heating to get additional leveling.

I did a couple of scraper coats to the opposite side yesterday. It was frustrating. Paul, I think I am seeing your point about my brand of epoxy being too thin for your tastes. I think I was using West on my first boat and the scraper coats were a breeze. The stuff yesterday was just sliding right off of my blade. Even on the stuff that wasn't vertical. I was doing the inverted tumblehome on the first build with no difficulty at all. I'm shifting gears right so I'm going to order medium and thick resins from my supplier and work on other things for now.

Speaking of changing gears, I've got a little more constructing to do now before I continue my work on fairing and finishing the hull. The day is approaching when I will be slicing the hull open for the centerboard case. My intent is to get as much structure in place before doing this to minimize any chance of the hull contorting due to relief of internal forces in the process. The plan is to make and install the case log for the inboard portion of the case and to apply the structural fillet and tape to the outboard portion of the case. The board is offset from centerline so there are inboard and outboard components and the components in discussion are all outside of the case. I'm filleting and glass taping were it's hidden from regular view and using a case log were it will be seen. I plan to add a piece of decorative trim to the top of the log to make it look like a piece of base mold. I may even match it on the other side of the cabin with similar, but less substantial molding. Most likely, I could cut the slot right now and not have anything shift. I'll be playing it safe because fixing a sproing just doesn't sound like any fun.

Today, I'm off to cut out the inboard centerboard case (The outboard portion is already a part of the structure.) and case log.

 

A hair drier, just doesn't get hot enough, you'll need a real heat gun. Even the cheap ones will usually have two settings, a lot hotter than a hair drier and way more hotter than a hair drier. Typically, the low setting in the 400 - 500 degree range, while high is 900 - 1,100 or so. I don't screw around with the low and just blast away on high. Keep it moving. A torch works just as well and yep, keep it moving.

You'll learn how high to jump indoors, once you've bumped your head enough grasshopper . . .

 

For flow coating foils with a clear epoxy finish the drier works spot on for me. Works fine on thin rovings and cloth too. Generally use relatively long set hardeners, which allow the air to 'flow' out. Even got one clear epoxy resin that is close to 24 hour working life. I've used the paint stripper gun before and it just pushes the coating thickness around so it becomes less even, for the use I mostly require of it.

I suspect that when you need more saturation through a (thicker or tighter) woven fabric the extra grunt from paint stripper or naked flame is exactly what you want. PAR is completely correct I'm sure, on the heavier duty end of this type of coating. More horses for courses than anything else.

 

I don't try to flow goo with heat, once it's on the work, just to pop bubbles. I admit to using a torch much more often then a heat gun. I find getting epoxy to flow is application more than technique. The right temperatures and tools will do more for flow than trying to move it around or flow it with a hair drier. The only time I have difficulty with this is vertical and overhead work, where I just use much thinner coats, applied as uniformly as I can. On relatively flat surfaces, I'll "flood" and let the goo do it's thing naturally. If there are special conditions, such as corners, where goo can pool or sag away, I'll treat these separately or bulk up with very thin coats.

 

On one of my smear coats the other day, I think that the fan I was using to blow fresh air into the shop was causing rippling on the epoxy I had just applied with a scraper. I'm wondering if thin epoxy is more susceptible air currents than a thicker epoxy.

 

Quite possible, those ripples may be down to that. It is getting the timing right that seems to be key. Perhaps I have been too conservative with heat, in that using a propane torch might be a bit risky with sawdust, shavings still around. Yup, I have seen sawdust go up a few times. It could well be flashing with the naked flame is enough to pop most of the bubbles. I'll clean the shop pretty well before trying it though.

I did find the paint stripper, because it liquifies the epoxy (with heat) led to it blowing the thickness around and was less even than the less vicous hair dryer.
As for application, probably used brushes, rollers, squeegees and scrapers, depending on the exact requirement ie clear final coat, or resin into cloth etc etc. In the end you seem to work out a way that works for you, and the conditions you have such as temperature.

Thanks for Hurricane Bertha btw, it emanated from PAR's neck of the woods. I sailed in it yesterday, not too fearsome after 4k miles....

 

By the time Bertha got to you, she wasn't much more then a nor'ester.

 

Back at it! Well, I've been at it. I've been too preoccupied to post. Here are some updates. I'll start with a couple of epoxied hull shots.



A third shot showing the results of scraping activities. I've been building coats and filling weave by rolling out the epoxy coats. This works well, especially with thin epoxy and builds the thickness rapidly. Unfortunately, it leaves a stippled surface than needs to be smoothed. Rather than make a lot of epoxy dust, scraping with a metal blade is a worth while alternative to sanding.



I've ordered some thicker epoxy that I plan to use with some final scraper coats, not to be confused with scraping the epoxy after it's cured. I'm wondering if alternating between rolled coats and scraper coats would build thickness the quickest. I'm thinking that the rolled coat would leave a stippled surface that the following scraped coat would try to fill. Another rolled coat following by scraper coats should round it all out. Oh so many thoughts and so little time.

 

How I spent my summer in Tobermory, ON.

A couple of thing to drool over. This preempts boat building.



Boat shadow in thirty feet of water.



I know, I know, completely off topic. I think of them as inspirational moments.

 

And now for some scary stuff.

After looking around inside the boat, mentally building the centerboard box, I decided that waiting to cut the centerboard slot was really going to add to the difficulty level of the process. I felt there was enough hull integrity to make this massive incision. I would take it take and check my progress to make sure the did not move irreversibly in the process.

Photo 1 is the pilot hole I drilled (lower center) from the inside of the hull from a known location and anticipated edge of the case log. The line was added subsequent to the hole. Note the seam/joint located next to the pilot hole. This joint location was planned as the actual cut line and was meant to provide a longitudinal axis reference for the outside of the boat. I made changes that I thought would affect the cut location, but in the end I ended up recutting along this joint. I did end up mis-cutting by this offset amount and will go into those details on another post.



All lined out.



The plunge cut. Scaaary!



The initial cut. I'm watching for any misalignments that might form as I'm cutting the lengthwise opening. Should any occur, I was prepared to add athwartship bracing to contain any movement. Fortunately, my concerns were unwarranted. There was no movement and only a slight bounciness that developed on the unsupported inboard hull. The inboard components of the box will reestablish the structural integrity here when they are installed.



The, sort of, final centerboard slot. I left extra meat at the forward end and will be checking drawing dimensions and, more importantly, board dimensions since it is already built to insure a proper fit when the time comes.

 

Some gratuitous interior shots with the centerboard components fitted in place.

Looking aft and forward in the cockpit, followed by aft and forward in the cabin. The last one is taken from under the cockpit and looks forward into the v-berth area. I've flipped all of the photos so they look right side up. It's interesting how the brain processes images depending on whether they are inverted or not.

 

Fixing a screw up and other stuff.

In the process of designing and building the boat, there have been a few changes along the way. One change was in the thickness of my longitudinals and centerboard box. These were originally sized at 3/4" and were subsequently reduced to 1/2" in thickness. These changes in material thickness have to be accounted for and corrections made. I thought I needed to adjust the location of my centerboard by a 1/4" when the reality of it was otherwise. I cut one side of my centerboard opening 1/4" too far outboard. Not a major mess up, time and energies had to be expended to get it corrected. Todays post is a pictorial of the fix and the structural joining of the box structure (longitudinal) to the hull.

The outboard portion of the centerboard box is one of two longitudinal pieces that run most of the length of the boat. These pieces are not straight, but follow a planned curvature and actually come together in the forward sections of the boat. This makes the width of the box variable and the forward sections of the centerboard were designed with a slight amount of taper to accommodate this feature. The width of the board is otherwise constant except this taper at the forward end and also the natural taper of the trailing edge. The slot is cut to accommodate the board profile so at the lower edge of the box, the planking extending past the edge of the box by a slight amount on the outboard portion. This was the area that I trimmed too much off. It here that I will ad some material back. My first thought was to add lots of layers of fiberglass to the area, but clear thinking soon prevailed. A strip of doug fir was added to replace the lost thickness.

This photo shows a layer of 17 oz. biax that I first layed across the joint.



This is the strip of doug fir bed in epoxy thickened with colloidal silica. This approach had multiple benefits. The original cut wasn't the best so when the doug fir was in place, it was very easy to trim it with a low angle block plane to true out the edge while setting the width of the slot.



Here I've filled either side of the fir strip with thickened epoxy and wrapped a 12" wide tape of 24 oz triax (+45/90/-45) around the joint. I've also applied a wrap of 7 oz cloth for abrasion resistance. I have only used axial fabrics in this build, but my limited experience with it has shown that a snagged fiber in an axial cloth can be ripped completely from the material. In a snag or abrasion proned area, it seems to be wise to protect your axial fabrics from these possibilities. Especially if they are lying under a finished area that would also suffer from this type of damage. As you can see in the photo, I did not completely cover the triax as I felt the upper portions would not be prone to damage.



Finally, the finished product. A little weave filling, a touch of fairing and a coat of epoxy. I most likely could have gotten away with a coating of epoxy, but.....



Also of note in the photos is the plywood doubler that is seen in the area of the frame. This narrows the box to board width plus clearance. I plan for lateral board loads to be carried in this area. The edge of the centerboard box was intended to line up with the doubler surface.

I'm close to putting in the second half of the centerboard box, but these tasks and others need to be completed or I'll create a bear of a situation if I get ahead of myself.

 

Well done, always a bit nervous when you 'open' the slot fully even when you know that it will not move!. On small sailboat hulls, one trick is to router out the slot but not fully, leaving short 'bridges' which maintain integrity until ready to cut slot fully. So if using an internal hog, this can be done prior to even laying onto the frames. If moulding/strip plank the internal doubler can be pre routed this way. It also allows you to find alignment from the outside, if you know beforehand that the internal (hog or doubler) is true. Hope that makes sense.

She's really coming on well, nice to see the details.

 

I gotta tell you, I envy you guys that can take a pile of lumber and build these things. I love being on the water and would really love to do a design to be proud of, but I just don't have the faculties for it. Looks like I'm sticking to the little stuff, for now, and will buy big when Mama hits the lotto.