Jump to content

Core Sound 17 hull #357


Dnjost
 Share

Recommended Posts

After combing over the plans, reading the forum, surfing the net, and viewing the photos on the cd over and over again, I am now ready to commence. 

 

I am planning on using Joubert Okoume panels and not glassing the hull to keep things as neat and light as possible.  How many builders have glassed the hull or at least the bottom?  I am really adverse to adding weight to what is a very light 18' hull. I recently glassed the bottom of a small skiff I built, and still question whether it was necessary.  I like the okoume panels as they come in at 98" long thus saving at least an extr sheet of plywood (small price overall, but it's the principle that counts). 

 

by the time all materials are amassed, the weather will perhaps be cooperating.   

Link to comment
Share on other sites

  • 3 weeks later...

Have decided on Meranti for the bottom (3 panels of 3/8) and Okoume for the remaining 9 sheets.  Aluminum spars as per plan with tracks.  

 

The design of the centerboard has me puzzled as I fear that as soon as water infiltrates the glass, epoxy coatings, the laminated structure will start to come apart from internal expansion.  Has anyone made a CB out of laminated plywood, or done a layup in glass to avoid this?  Perhaps I am being a tad too obsessive compulsive here. What wood has everyone used for this?  Finding suitable thicknesses of Mahogany or Fir may be the best bet,  Construction grade spruce is very easy to find locally.  I just don't want to spend hours shaping a blade and have it self-destruct.  I am actually considering building a board out of foam, shaping it, and them making a mold to cast two fiberglass halves in.  Might be more durable.  

 

David Jost

Link to comment
Share on other sites

The design of the centerboard has me puzzled as I fear that as soon as water infiltrates the glass, epoxy coatings, the laminated structure will start to come apart from internal expansion. 

Why will water infiltrate the epoxy coating?  If enough damage occurs, then it is prudent to remove the centerboard and repair it rather than contunued use which may lead to problems due to expansion from moisture.

 

Laminated plywood is no where near as strong as half (or nearly) of the layers have the grain running in a direction that does nothing to oppose the forces on them.  Solid wooden boards have all the grain in the right direction to resist breaking.

  • Like 1
Link to comment
Share on other sites

My CB is laminated out of wood strips. Then I cut the front of the tip off (diagonal cut about 3"-4" at widest point) and then epoxy the tip back on. Theory is if you drag the board on an abrasive bottom and shave off the epoxy/glass coating the water sucked up will stop at the glue line. Of course the entire board is sheathed in glass cloth.

  • Like 1
Link to comment
Share on other sites

Junk wood as far as *marine* quality as viewed by a purist. Basic lumberyard construction SPF (spruce/pine/fir) 2X whatever, surface planed and ripped into square strips. I marked the wood before ripping and then flipped every other piece end for end and rotated a few to get the cross grain orientation I liked, then slobbered Titebond III on them and racked them up with several bar clamps. The alternate end for end flip is supposed to equalize warp stress and result in a stable laminated board. Must work because my roughed out blank has been laying around for about a year and is dead straight.

The fun part = shaping the blade to an NACA airfoil, yet to be completed. I used a router w/edge guide - the router path of travel was longways on blade - and dialed the bit down as I moved toward the edge, leaving a thin (1/8") "rib" at full thick to support the router. Result: a blade with roughed out grooves which will simplify the planing, grinding, and sanding process to achieve a nice foiled blade. Haven't started that dusty part yet - got sidetracked building stand up paddle boards and kayaks for darling Daughter.

My finish plan is one layer of 6 oz fiberglass, doubled at leading edge and tip, weave filled with resin with graphite filler. Unless one is measuring micro-knots I doubt the graphite coated blade is much of a performance enhancement but it looks really cool.

Link to comment
Share on other sites

I did just find 2X6 doug fir at my local yard!  got plenty of West and glass.  Funny you should mention the graphite.  I have done several blades with a graphite coating.  It works well on the racing circuit.  I actually did the whole bottom of the hull and saw a statistically viable increase in speed,  It also helps the hull slide on and off the trailer. This can be done later on if we get into wishbone rigs and carbon spars and laminate sails.  (part of the reason I gave up racing the phrf circuit was the ongoing arms race). 

 

I like the diagonal cut, makes sense. and doesn't add a ton of time.  just more glue used.   Off to the lumber yard, then the table saw.  and voila!

 

  just noticed the knot.  will cut a replacement strip.  doing strip building allows to toss the questionable pieces. 

post-2815-0-02273900-1362848747_thumb.jpg

post-2815-0-42053700-1362848748_thumb.jpg

Link to comment
Share on other sites

Have decided on Meranti for the bottom (3 panels of 3/8) and Okoume for the remaining 9 sheets.  Aluminum spars as per plan with tracks.   David Jost

 If you wouldn't mind sharing... is the 3/8ths specified in the plans? ...or is that you choice for some reason? THXYes. CS-17 plan calls for 3/8" (9 mm) bottom panels aft, as in about the last 2/3rds of the hull. Froward sections are 1/4" (6 mm) as they have some bending to do.
Link to comment
Share on other sites

yes.  the suggested layout has the three bottom panels laid out on 3/8 plywood.  and the sides and other plywood pieces laid out on 1/4" (6mm).  Graham also show the rudder blade being made of  2 laminations of 3/8 as well.  the layout show, allows for easy splicing of the three sheets of 3/8.  Having 98" Okoume for the sides will allow for splicing without having to purchase more plywood, so is worth the cost.  

 

Fir is in garage and first cut to begin on the cb construction.  

Link to comment
Share on other sites

CB looks good. No need to sweat the knot in a strip laminated build unless it's loose. I strip build my rudders as well using Western Red Cedar. Those I finish clear = pretty. The rudder blank is thick enough to carve an NACA airfoil shape and before shaping I use my router to shave down the top section to fit into the cheek blocks of the rudder assembly. Sheathed in fiberglass they are fairly strong.

The wood epoxy 14' catamaran I built was sitting on the beach with the mast stepped when a T-Storm ripped through and a the 50+ wind gusts flipped the cat end for end twice. According to witnesses it was quite a show. Only damage was a rudder. The tip where the ash tiller was attached broke off. Took me maybe ten minutes after the wood dried out to glue it back together and lay another layer of glass on it = good to go.

Note: I use Titebond to glue up strip blanks because the sawed parts fit tight and are clamped tight which is not a good plan for epoxy glues since they like a pencil line width glue line whereas the tighter you squeeze the better Titebond likes it. Some folks mix ground walnut shells or the like in epoxy to provide "shim" to form a thicker glue line, I just stick (pun alert!) with Titebond for tight clamp jobs.

Link to comment
Share on other sites

I used Titebond III for the rowing cleats on the Michalak Vireo I built last year.  Still good after a season of hard rowing.  I like the walnut shell idea, I do have an electric coffee mill that would do the job of getting the shells milled but not too much.  too bad I just threw out the Christmas walnut supply.  laminated board is in the basement waiting for gluing. i was able to arrange all of the strips so that the funky ones were outside the final finished shape. 

Link to comment
Share on other sites

I have only epoxy glued the CB's I've built. Titebond III might work well, as might something like DAP Weldwood. These presume you have good joints and can clamp the snocker out of it, which normally you can do with such a layup. A secondary reason to use glue is to make it easier on edge tools when shaping.

 

One critical step is to make sure that whatever the layup rests on when clamped is dead flat. If you spanned a couple sawhorses, for example, and the two crosspieces were not dead level, you could build in a twist. I have two of these to do and I've been eyeing the new granite kitchen counter tops, as they are stable and dead flat. Hopefully I'll remember to put down plastic everywhere or I'll have to look for a new place to live.

 

On the walnut shell, no need to make your own. It is commercially available in a variety of grit sizes. I've found the 30/100 grit to be about right. The 30/30 grit is often used as non-skid additive to paint. It is pretty coarse for glue shim use. It would leave you a wider joint unless the wood you are using is soft enough that the clamps will drive it in. Secondary benefit, beyond the shim affect, is it locks the joint in place to keep it from sliding around.

 

http://www.hammonsproducts.com/page.asp?p_key=11C0327901AC464D852200F057E1E6B5&ie_key=093275B1163E451EA575A79C8E796C51

 

Similar products are also sold on Ebay. It doesn't take much. A pound would probably last for years.........if not a lifetime.

Link to comment
Share on other sites

I still have it in the glue cabinet.  probably will never use it again (thirty years old for first boat).  but...that boat is still going and on it's third owner and second generation. 

 

Now...have become obsessive compulsive over the NACA foil shape for the blade.  Things look pretty straight and true so far.  No twist.  will build a jig for the router to cut the foil shape.  Looks straight forward. 

Link to comment
Share on other sites

  • 1 month later...

I am getting a tad OCD on this. but having a blast.  Was going to get the plywood tomorrow in Somerville, but will stay out of the city tomorrow.  Phone order.  Would love to hear comments on this approach.  The taper messed with my original idea of routing the shape off a halo around the foil shape and moving the board through the router template/table.  will plane to lines.  Below is from the blog I am keeping of the project. 

 

The Centerboard has been roughed out to it's approximate final shape and I have become a tad obsessive compulsive regarding the final shape.  The photo shows the NACA 0008 shape as it seemed to fit the final shape of the tip of the foil the best.  the NACA 0009 might be better.  My plan is to set a dado router bit to the depth indicated by the template and then  set a guide for the router to follow.  I will set the guides as expanded lines up the foil at several stations as the template can be expanded to fit the width at each point.  I used the plotter at http://airfoiltools.com/plotter/index  be sure to select "no margins" on the printer or things get compressed.  I can generate a NACA foil for several points along the board and then connect the points to expand the lines through the taper.  The router would then follow the lines to cut the lines to be planed to.

 

 

Posted Image

 Area that will be inside the trunk is clearly marked.  router will be used to go vertically up and strike marks to plane to.

Posted Image

 I have no idea how I will shape the tip, other than just rounding it off.

 

Posted Image

Link to comment
Share on other sites

The hand plane will be used after I rout to the proper depth for guidelines to plane to, then smooth with belt sander and random orbit sander.  Opinions appreciated, thanks.  

 

I am making a series of plywood templates to test the shape that fit at various increments along the taper. 

Link to comment
Share on other sites

Never tried this, but I have heard of people using their circular saw to cut guide depths. They start out very shallow, then reset the saw guide and depth and make another cut and so on. Then you can just knock out the thin strips left and belt sand her to an almost perfect shape. You will have to do the tip completely the old way though. Also this wont work with a curvy board such as a rudder.

Arch Davis uses this method to hollow out masts. Much faster than doing birds mouth strip build mast.

 

Scott

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.