Rat's 1977 Polar Kraft 1440 refit

[Rat]

Sintra is an expanded PVC board, similar uses to plasticore but a little (!) better specs.
tech specs here:
Sintra specs

Basically it has pretty good shear strength and modules of elasticity, making a good fastening system is going to be a chore tho. It will proly need to be framed and bolted or screwed, no glue joints or epoxy. And it needs to be treated for UV protection although the specs seem to indicate it is for color fastness not due to elongated structural failure. But still, it's PVC and needs to be protected I would think.

Weight by comparison is good:
1/2 ply 1.5 pounds per square foot
1/2 Sintra 1.34 per square foot
(and you would still need to add more weight to the plywood for weatherproofing.)
It has 1/2 deflection for 30 pounds on 60 inch centers, which equates to roughly 20 inch centers for a 200 pound person standing flat footed so 14-16 inch centers would likely yield very little, if any, deflection.

It also has a low resistance to benzine (fuel).

The cost is the most prohibitive spec tho!

For my style of building if I am going to spend the money anyway, I will use honeycomb, Nidacore or Divinycell if I have to. But my first choice would be 1088 Marine Ply, it just has better specs and is more suited for my style of building.

I think Sintra would be good for decks and soles that are going to be covered with Durabak, carbet or paint but aren't going to be structural or handle any shear loads; keeping in mind the few negatives so they can be engineered to a safe level. Also, since Sintra is made to be covered I think a good adhesive backed grip tape may be the best option for getting a good uniform, lasting no-skid surface.

I say try it and let us know how it works for ya! :mrgreen: Plus they have a TON of cool colors.
Sintra website

 

[huntinfool]

Bobberboy has already used it. I'm trying to go as light as possible with anything I put in my boat. I already know what I can do with resin and glass and even epoxy for that matter. What I want is something that is lighter and will last longer. This might be it. They have another product called epanel which is aluminum on both sides of a core, but I have a feeling it will be expensive. Besides I want to try something new. As I said before I workwith glass every day and I know what it is capable of. I just really want to try something new. I'm still looking and not sold on any one product yet.

So far your boat is looking good. When you get it done we need to plan a hunt/fishing trip and test it out.

 

[Rat]

The X-Treme Hunt is coming up in February. You need to be there!

No leaks in the boat as of this morning. It started raining about midnight last night and, since I don't have the cockpit drains in yet, the entire cockpit is about 2/3 full of water! #-o

I'm just happy it's raining.

 

[huntinfool]

Time for a bilge pump!!! Good to hear that it doesn't leak. Just remember to seal the wood where you put the drains in and use plenty of silicone where you put screws in.

I've tried to make the big hunt several times, but it always seems that something comes up. I may just have to mark the calendar and make it happen this year.

 

[Rat]

Pumped the water out when I got home; it never got more than half full (half empty?). The water ran out thrpugh the electrical conduit into the bilge area and drained out, I only had to pump about 20 Gallons!

 

[huntinfool]

If you only knew how many times I have had to do that. It never fails I pour a solid glass transom and the next day it rains and fills the boat up with water. Luckily in that case I can drill out the drain hole and drain the boat. Other jobs I have to get the bilge out.

 

[Rat]

In between picking up boats and fishing this weekend I did manage to get a little work done on the tinny. Earlier this week I got the cockpit drains cut in and sealed up; today I did a little fairing. I sanded everything down, washed it off with water, dried it and added the last bit of fairing compound to her. She isn't going to have a yacht finish, but I didn't want to leave the glass ends showing either. I'm not going to fill the weave in the cockpit either, just add another seal coat and then paint it with non skid additive. She will be ready for paint before long. I have a few more details to work out like the wiring box, battery and fuel tank locations and final seat arrangement. But I need to order more wood flour and epoxy, I am down to my last half gallon and completely out of wood flour.

This weeks photos:

 

[huntinfool]

Coming along nicely Rat! Looks like you will have alot invested in this. It is going to be so worth it when your done to have a boat rigged just like you like it.

 

[CHILIDWG]

Looks good Rat!! Thanks for the foam idea.

 

[lowlight]

I noticed you are using 1/2 inch ply? Is this only because you are glassing it or is 1/2" a common suitable way to go?
The foam idea ROCKS! Thanks for the tip. Your boat looks very nice, thanks for sharing. I'm eager to see the outcome.

 

[huntinfool]

1/2" ply with glass over it is very strong for a floor. It will be more than anyone will need on an aluminum boat. It will make the hull stronger once secured to the ribs.

 

[Rat]

Just an update everyone. I haven't done a single thing on the boat since my last post! I have been fishing, hunting, hiking etc; plus it has been raining every other day. But I have a fresh batch of materials and I am going to be doing some work over the long weekend. I am anxious to get her done now, so no more lolly gaggin' around!

 

[dyeguy1212]

since youve been so lazy, you should make up for it with a thorough explanation of what the heck you did to that ply wood.. I'm still lost..

 

[Rat]

since youve been so lazy, you should make up for it with a thorough explanation of what the heck you did to that ply wood.. I'm still lost..

Well, since you asked...
The process is called wood core composite, it is a fiberglass sandwich.

The plywood is simply being used as a core material, there are lots of core materials out there, DinaCore, DivinyCell, many options. The core offers some of the strength on the framing or the hull, depending on what it is used for.

The epoxy is a medium where a highly stable cross linked polymer bond is made; it is very strong along many points of elasticity (shear, impact etc.). Epoxy is two part, Epoxy and Hardener, and comes in different mixing ratios. I use MarinEpoxy witch is a 2:1 mix.

Fiberglass is a very strong cloth like substrate, we are all familiar with it to some degree. Mostly on Auto body repair. It is a cloth matt and the direction and lay (warp and weft) of how it is woven is also how it is named. Bixial is woven with the fibers in a 45° angle to each other, matt is woven with the fibers in a 90° angle to each other. There are various names for each weave according to weight and finish and a few other factors. Matt can also be from Kevlar, or carbon fiber, as well as other high tech fibers. Fiberglass is best at absorbing Epoxy well, is relatively cheap and wroks for most of the design specs we will ever use it for, including safety factors.

So basically what I do with my plywood is one of two things:
1) Just coat it with epoxy. This is to keep it watertight as well as add structure to the wood. Used mainly in frames internal bulkheads or areas where there isn't a high degree of traffic (walking, dropping anchors etc).
2) A true composite sandwich. IOW, from top to bottom you will have this: Epoxy paint, Epoxy primer, Epoxy fairing compound, Epoxy, Fiberglass encased in Epoxy, another couple layers of epoxy, wood core, A couple layers of epoxy, fiberglass encased by epoxy, two more layers of epoxy. That is a full composite sandwich. For my little tin boat I leave off the bottom layer of fiberglass as the sole isn't structural, I just want the fiberglass for strength when i drop something heavy and for added protection from normal wear and tear.

The goal is to encapsulate all the wood so no water gets in. Epoxy resin is waterproof, not like Polyester resins which will allow water intrusion. If you totally encapsulate the wood, no water gets in and therefore, no rot will ensue. Adding the fiberglass matt adds great strength to the sandwich, just add it where it is needed.

All screws will have 5200 in the holes, or be overdrilled, filled with epoxy glue, and then drilled smaller so as to not allow any water contact with wood, ever.

Using epoxy/fiberglass will allow you to use smaller core materials for the same, or better, strength to weight ratios than single component hulls/decks.

Does that clear it up? :LOL2:

 

[dearl]

Uh yea, I understood every word, I think..... Make a long story short, and tell everyone your boat will be built like a tank, and wont rot! They will understand that.
Like I said before you guys that can work in fiberglass have a gift, I tried it on a 72 Grady white, and did good till it came to cabosil, and wood flour, and biaxle, woven roven, lost it mid stride, give me something I can weld, or burn, I'm good, mixing the proper amount of hardner, and getting the right mat or chopped strand, I'd probably glass myself to the bottom of the boat. Look like a fly stuck to fly paper. :LOL2:

 

[Rat]

Because the weather has been so uncooperative I have been sweating the details; sanding when I can and touching up epoxy and fairing when I can. It's tough between rainshowers, or you get an unexpected one and hafta sand off all the epoxy with Chicken Pox! I am working on my Tinny outside as I have the workshop full of GF-16 (my other boat) at the moment.

So this has left me with plenty of time to contemplate seating arrangements, batteries, fuel tanks and such as that. I have it all laid out in my mind, I just need to get it transferred to wood, glass and epoxy. I am still working on the lighting, not sure how I am going to go on that yet either. I also need to get to work on the engine...

Anyway, I am making progress, just in small amounts, a little here, a little there; eating an elephant right...?

 

[dearl]

Yep, staying pretty wet here too. Just look at it this way, you'll have all the details worked out, and you can steady go after it when the weather breaks. If your like me you'll run out of money long before you run out of ideas.

 

[Rat]

I have been waiting to cut the aft deck hatch because I wanted to use a prefab hatch, but I haven't been able to find one that would fit exactly; so I cut the hole today. I cut the hatch opening, battens and hatch stringers, coated everything up with resin and it is drying.

I think I have my batteries figured out as well. I really didn't want to have a battery in the forward locker, but I am going to put one there. One in the forward locker and one in the aft to Port. The fuel tank will be in the cockpit and be movable as ballast when needed.

I also started the wiring today, just the wires, I still need to order the switch panel, lights, 12V sockets, buss terminals and fuses. I have all the other hardware, but still need to build the rod holders. As soon as I figure out which seats I am going to use I can put down the blocks and then I can paint, if it warms up enough that is.

I also figured I will need to rebuild the trailer, the hull doesn't fit. I need to lengthen the tongue by three feet to get the transom on the bunks at the end of the trailer. It will work for now, but if I have the extra cash I will do it before first splash.

All it takes is money...and time.

 

[dyeguy1212]

Thanks for the run down rat, I understand now. I think I'm going to use epoxy resin on 3/4" ply wood, and save myself the impending doom of dealing with the glass process. Interesting read though!

Out of curiosity, how much does that process run you, and how much money (and weight) are you saving compared to thicker ply or sheet metal?

 

[Rat]

Thanks for the run down rat, I understand now. I think I'm going to use epoxy resin on 3/4" ply wood, and save myself the impending doom of dealing with the glass process. Interesting read though!

Out of curiosity, how much does that process run you, and how much money (and weight) are you saving compared to thicker ply or sheet metal?

Here is how the weight breaks down for my refit:

I estimated the weight last night.
91.75 pounds of 1/2 ply (I used 7/16 but don't know the weight of it, so it will be a little less)
12.00 pounds epoxy (2 gallons) includes fillets/glue
1.0 pound 12 oz glass
12.0 pounds of 1x2 (approx 40 linear feet)
2.5 pounds two part foam

120 pounds additional so far (give or take). This is in addition to the hull and doesn't include the transom rebuild.

Most of the heavy stuff is done so I am thinking the hull will end up around an additional 150 pounds with hardware.

Compared to Alu. I think the composite method is pretty close in price. I don't really know because I have never done full refit using Alu; just repairs and small add-ons to some hulls.
The Pros are that wood core gives you a measure of flotation, is more impact resistant, puncture resistant and has a better elasticity modulus.
The Cons are it could get rot if not properly installed, takes longer to install (no way around cure times), and has a steeper learning curve as most people already understand metal work but not lamination work.

I have seen stitch and glue hulls that weigh close to 2/3 what the same hull in alum weighs. IE a 16 foot 48 inch (at the chine) jon boat that weighs 170 pounds. That's a custom built composit Vs. a production Alu. hull.

Compared to heavier ply and water sealing it is lighter but more expensive. You need a lot of framing to add structure to non composite wood that is not needed with a composite sandwich. Look at the images under my fore deck, there are no braces or kickers; just a cleat around the outside and a rear frame with a stiffener. Wood sealant isn't very lightweight, but it is lighter than epoxy/glass, about 4-5 pounds (?) per gallon for sealant Vs. 6 for Epoxy. Gallon for gallon it is lighter, but you need more of it and you need to cover more wood (framing etc).

So far I have used about $120 in wood and will end up using about $170 in Epoxy and proly $15 in fiberglass; add another $30 for stuff like woodflour, mixing cups and latex gloves. So around $335 by the end of the build. This just includes the composite stuff as I would use the same amount of 5200, 4200 and foam. The topside paint is going to run about $200 Vs. what it would cost for carpet like many people have.

For me, I just like the "feel" of a composite boat over an all Alu. boat; and I like the durability better than just a sealed wood and carpet inside. Any three of these types will last a long time if done correctly and maintained.

So to answer your question. I'm not saving any money, it is more expensive than wood sealant and proly close to the same cost as Alu.; but I am saving weight over both methods.