Replacing Balsa Core - Few Questions

[Salmon Fisher]

Good work on your part. I always enjoy reading about how others approach problems and then work through to a solution.

As for uploading photos...you need to request a photo album from one of the C-Brats excellent owners and moderators:

TyBoo

At the top menu bar to the far right is "Help" just click on it and the first topic is how to request for your photo album.

Then there are instructions on how to upload your photos.

[Salish_Explorer]

Uploading pics on this board requires admin permission, as noted above. However you can post links to services like imgur I think (just not inline photos).

Barring damage from groundings, water intrusion/core damage is almost always from improperly prepared topside penetrations.

If there were sufficient hull damage to allow water penetration from the outside, you'd almost certainly see it. Fiberglass crazes, it develops stress cracks and sometimes even blisters - but it doesn't just spontaneously spring leaks, anymore than a Tupperware does. It leaks where someone has put a hole in it.

Don't overthink it.

[thataway]

First a question for Tom: Tom, have you taken delivery of your electric C Dory 22? If so, please give us some photos and numbers.

[Salish_Explorer]

One other thing I'd add, since it seems like you may be new here, is that two of the people posting on this thread (thataway and Marco flamingo) are pretty high up there among the amazing sources of knowledge on this forum for taking c-dory's to the max. Bob has truly lived the boat-lover's dream with all kinds of adventures, and Marco (a PNW'er) like you and I) has taken his 16(!!!) to places I only dream of, from the broughtons to the potholes.

Marco also has some really great photo albums of upgrades he has done to his, including adding a permanent fuel tank like you mention.

I really am interested to see whether you do the tank, and if so, how. By my read that is maybe the single biggest bang-for-your-buck upgrade to the smaller hulls, which otherwise hit their tankage limit pretty quickly. Other than electronics upgrades, it's the one big mod I'd love to get to this year.

[Pburk]

Ok. I got a first round of photos up! I'll follow up with some additional images this weekend.

I'm going to glue down the first layer of 3/4" balsa this weekend assuming the weather cooperates. It's tough to scribe the balsa to the edges, there's lumps of whatever filler used to be there and the scored balsa doesn't shape quite like a piece of solid wood (and pieces fall out at the edges). Trying to decide if I need to recut some of these pieces to get tighter gaps or if I should just plan on filling these voids with a couple lifts of epoxy.

Regarding the fuel tanks, I've been making some models of Moeller tanks out of plywood and 2x's to test fit them. Trying to decide what would be best. I've found a couple that work in the direction in Marco's gallery, but none of them have the capacity I'm hoping for. Has anyone just tried a belly tank running toward the bow under the berth? It doesn't get the plumbing as tight to the side of the boat, but it seems like there are more options that might fit and I'm planning on plugging the notch for the head.

This might be silly, but one concern I have with a belly tank (like the Moeller FT2740), is if the fuel is spread to thinly across too much space. I have a vision of being low on fuel and it causing problems that the gas is sloshing across a 50" length. Is that a valid concern? It would be really awesome to have 50% fewer trips to the fuel pier this year.

[thataway]

The photos sure help in many ways. That was severe core disruption you found by the screw holes. Had the boat been through a number of freeze thaw cycles? Especially if the boat was left out in freeing areas. Was the boat run hard? I realize that you cannot answer these questions, and if you cannot find out, then are rhetorical.

How wide is this gap between the new balsa and the remaining core at the very edges--or is there remaining core outside of the new core? You can fill these areas with a light filler and epoxy mixture. For example microballoons come to mind. I have seen failure in micro balloons on outside fairing after many years--I don't think that would be an issue here, and my recollection is that the microballoons were with a polyester resin in all cases--I might be conflicted here by the choice of polyester for the filler combined with microballoons and cabosil...because of the much higher cost of the epoxy. I would mix some cabosil in with the microballoons.. Both of these are appropriate repairs. I would limit this balsa unfilled area to less than 1/2" in width if possible.

An aside: often when putting structural bulkheads onto a boat, foam is cut in a trapezoid shape to stand the bulkhead off the hull for about 3/8" to 1/2" so the bulkhead is not a hard place in the hull, and could cause fiberglass fatigue. We then would build the filet and put in 3-4 layers of tabbing of cloth/mat to secure the bulkhead on both sides. You might consider the floor, in being somewhat similar to a bulkhead, and bring the top layers of glass concentrically up the side of the hull (in our Caracal, we will be leaving 2 to 3" of the old "floor" along the sides, and then sweep the new top layer over this and up the sides of the hull.) For building bulkheads we would first use a "tic board" to find the rough contours, then make a cardboard template, double check its fit before cutting the marine ply we were using as the bulkhead. One could use a laminate panel as a major bulkhead, as I believe Tom Hurby noted that his new C Dory 22 is being built with a hollow core material in at least part of the construction.

Does anyone know what the original laminate schedule of the C Dory 16 floor (inner aspect of the hull) was? Today I would probably go with a of layer of 1708 and 1808 each. That would be a very strong floor-perhaps stronger than the initial laminate. This series of laminates use bi-axial fibers: 1708 bundles of fibers are at 45 degrees. The 1808 fibers are at 90 degrees. The 1708 goes around corners more easily. But there is difference in panel strength between the two.

In the past the builders might use a layer of roving (18 to 24 oz) in the inner aspect of the floor (hull bottom), The outer laminate should have at least one layer of 18 to 24 oz roving when first built. Today with the biaxial and tri axial cloths there may be a different laminate schedule and a good chance the boat would be lighter as well as stronger.

[Salish_Explorer]

Just checking back here, how's the progress going?

In regards your question about locating fixed fuel tanks: There really only seem to be three options. One option is clearly not great, the other two would seem to each have their advantages.

The first option is bow placement. Moeller's 19 Gallon Bow Tank looks just a bit too tall to fit under the existing v-berth sole in my 16, but I think it would work fine if I tabbed in a new sole a few inches higher.

Option 2 is stern/splashwell placement - they changed the layout of the stern on the 16 between the Classic (mine) and the current design (yours), but either would accommodate either one or two (split) stern tanks lengthwise at the transom. Obviously, in the modern design it's a bit of a like-for-like swap, since you can already place portable tanks there, but I think you'd get ~50% more capacity and of course easier fueling.

The third option would be a pair of vertical tanks along each gunnel amidship. I think this would be the most complicated option, in terms of fiberglass work, and would buy you the least additional capacity.

The major question I see is weight distribution: at 6 lb/gal you're looking at adding 120 lb quite far forward, vs. at the stern.

I flatly don't know which would be better. The 16 Cruisers like some additional weight up front, but the Anglers* are fairly balanced, and even suffer in some cases from 'chine riding' - the tendency to dig and hold chine at speed if over-trimmed, which is scary and dangerous.

Since it's the result of too much bow-down trim, chine-digging is easily avoided by simply easing up (trimming a bit more bow-up).

It doesn't seem like rocket science that adding 100+ pounds at the bow could in certain conditions exacerbate that tendency, and make it harder to correct.

Allllll if that being said..... Marco has actually done this mod, and I've always been curious to get his take on it. And of course, if you've hung a 60lb kicker off the transom like I have, then it probably cancels out.

[ssobol]

As mentioned, weight in the bow of C-Dorys can help the ride in some situations. The problem becomes that if the situation changes and you need to get the bow up, you may have a hard time getting rid of the weight in the bow if it is something like water, fuel, or chain rode.

Trim tabs can get the bow down, but can't really get lift it up. They just counteract the bow up tendency of the boat.

[ssobol]

As mentioned, weight in the bow of C-Dorys can help the ride in some situations. The problem becomes that if the situation changes and you need to get the bow up, you may have a hard time getting rid of the weight in the bow if it is something like water, fuel, or chain rode.

Trim tabs can get the bow down, but can't really get lift it up. They just counteract the bow up tendency of the boat.

[ssobol]

As mentioned, weight in the bow of C-Dorys can help the ride in some situations. The problem becomes that if the situation changes and you need to get the bow up, you may have a hard time getting rid of the weight in the bow if it is something like water, fuel, or chain rode.

Trim tabs can get the bow down, but can't really get lift it up. They just counteract the bow up tendency of the boat.

[Salish_Explorer]

Also, like you are thinking I moved my battery.

I went back and forth between having it in front of the helm or in the footwell between the front seats. I had been planning on the former, but when I tried the latter just to see, it actually was not nearly as annoying as it would sound, and it's a good foot Lower and obviously dead on the kielson, so a better placement from a weight/roll perspective.

[Salish_Explorer]

[Tom Hruby]

To answer the question from Thataway - I expect that my C-dory will be finished sometime by the end of the month. After that I will need to spend some time altering the cabin to add a second berth under the helm seat. NMI is building the starboard side of the cabin with the platform running the entire length of the cabin. I hope to be on the water by June. We have not yet figured out how to place all the different equipment needed for electric propulsion. I plan to spend a few days in Bellingham mounting the motors, batteries, etc. there to work with the C-dory folks in case they are interested in further marketing of the electric version.

[thataway]

Thank. you Tom. I apologize, I know that you gave the amp hours and voltage of the LiFePO4 batteries-could you include that again when you put the performance numbers up.

A number of us are very interested in what your numbers will be. Also if you would not mind sharing, the cost for the electric motors and batteries, vs the cost of a single 150 hp Outboard--which would probably in the 8 K to 12K plus cost of binnacle, display, and associated rigging costs of from 2k to 3.5k...(I checked and Suzuki 115 is about the same range.)

As to the bow weight. I tend to keep the bow as light as possible. It is fairly easy to drive the bow down with tabs and a Permatrim. There are times I might run in following seas which the average C Dory owner might not try. (Disclosure, I have not owned a 16 of any vintage, so I am generalizing all C Dorys in the same "basket". My wife would not give her blessing of the 16 as our last C Dory; the ride in the Caracal Cat is so much better than any of the C Dory monohulls, and equal to the Tom Cat, maybe slightly better because of the higher tunnel clearance, with almost an identical hull profile and a length to beam ratio which is better (8+', with 18 LOA. and 8 1/2 with 27' LOA.). Ideal Beam to length should be more than 1:3.

The more weight in the ends of any boat, there will be more of a chance of handling issues, and less efficient ride. The reason when adding extra batteries, I put them in the cabin (not FLA batteries.) and try to avoid the aft most areas.

[Pburk]

Hey all,

Sorry for the long delay. I had a couple other things pop up, but have started epoxying down the balsa. I haven't been able to dedicate a chunk of time to it so I have kind of been sneaking off to glue down a couple pieces now and then. Slow going but it is getting done.

I will say, I really wish I had been able to find 1 1/2" balsa! It's hard not to look at the single layer of 3/4" and day dream about how I could just be done right now, not to mention the small fortune I am spending on epoxy! I keep telling myself that properly glued with staggered joints the two layers will be stronger but, I'm not an engineer, so that might not even be right. That said, if I'm wrong please don't correct me..I need the motivation!

I'll try to get some updated photos up soon. Thanks again for all the advice, it has been super helpful.