Lightweight netting beams?

[Frank Olsen]

In my Pahi31 rebuild I'm now ready for 2 new netting beams.  The old ones were as plan made out of Douglas Fir  and were quite heavy, 2 layers of 1-1/2" x 4" with 3/4" blocks sandwiched in between.  My boat was always too heavy and I'm trying to lighten her up in this rebuild.  The bow netting beam also had the forestay pulling up on it and I had a seagull striker cable to resist that pull which is the method JWD designed for the Tiki rig upgrade.   The stern beam has very little loading except for the netting itself and I think it could be much lighter than the plans.

Anyone have any ideas for light as possible Pahi netting beams? I've thought about aluminum tubing or possibly a foam core composite beam of sorts but wouldn't have a clue as to how to design it.

The overall length of the new beams needs to be 12'-6" with 12' centers for the bolts.

Thanks,

Frank

 

 

 

[kim whitmyre]

Frank,

For my t26, which is 2' narrower, I am using a 1/4" x 2 1/4" aluminum tube for the aft netting/ladder beam. This section is exceptionally stiff: I regularly sit in the middle of it and it shows no deflection. Here's a shot before I added teak plugs to the ends:

http://farm3.static.flickr.com/2456/3951588710_c36baef93d_b.jpg

On the tikis, the forestay is bridled to u-bolts on the bows themselves. It would seem (best to ask Mr. Wharram's shop) that if you could keep the same geometry, the tiki method would solve the forebeam problem.

[Frank Olsen]

Thanks Kim for the reply,

I did send an e-mail to JWD about aluminum, haven't heard back yet.

As far as using a bridle forestay arrangement I like that idea and did analyze that a bit.  I realized I'd have to position the ends of the bridle cables quite low at the bows, quite a bit below deck level in order to keep my original headstay and furler length, unless I raise the mast tabernacle equally, which is not out of the question since I will be building a new tabernacle.  This might be a good idea anyway because it will give me a little better headroom under the main.  I've noticed that boatsmith's Tiki 30, which has the same rig as mine, seems to have a slightly raised mainsail in order to clear the bimini roof.  I see in your photo's that you have a dodger of sorts, did you have to raise your main any to clear that?

Thanks, Frank

kim whitmyre said:

Frank,

For my t26, which is 2' narrower, I am using a 1/4" x 2 1/4" aluminum tube for the aft netting/ladder beam. This section is exceptionally stiff: I regularly sit in the middle of it and it shows no deflection. Here's a shot before I added teak plugs to the ends:

http://farm3.static.flickr.com/2456/3951588710_c36baef93d_b.jpg

On the tikis, the forestay is bridled to u-bolts on the bows themselves. It would seem (best to ask Mr. Wharram's shop) that if you could keep the same geometry, the tiki method would solve the forebeam problem.

[kim whitmyre]

Frank,

Here is a shot of the location of the u-bolt location for the bridles on the tikis:
http://i929.photobucket.com/albums/ad131/kgwoo/Vaea/IMG_0004-2.jpg

It's almost halfway to the water, down the line of the bows.

The main cleared the dodger by about 4" with the original mast. It's a low dodger, just enough room to sit under.

[Frank Olsen]

I just heard back from Hanneke about aluminum dimensions, here's what she suggested:  "We used a 4" diameter tube with 3.5mm wall. We used a 5" diameter beam on the Tiki 36. You could use an oval section placed vertical, i.e. greatest depth up and down".

kim whitmyre said:

Frank,

For my t26, which is 2' narrower, I am using a 1/4" x 2 1/4" aluminum tube for the aft netting/ladder beam. This section is exceptionally stiff: I regularly sit in the middle of it and it shows no deflection. Here's a shot before I added teak plugs to the ends:

http://farm3.static.flickr.com/2456/3951588710_c36baef93d_b.jpg

On the tikis, the forestay is bridled to u-bolts on the bows themselves. It would seem (best to ask Mr. Wharram's shop) that if you could keep the same geometry, the tiki method would solve the forebeam problem.

[Randall S Anselmo]

Frank,

For aft netting, boarding ladder and solar panel support on our Tiki 26, we used bamboo.  It was very light, very strong and very free when I asked a neighbor's permission to cut a single stalk from his yard in exchange for cleaning out some dead bits.  I can't comment on the durability just yet, but given the replacement cost, I'm not too concerned.  The span was about 10 feet, diameter was about 3 inches, and the variety was "Painted Lady"...very attractive at first, but lost its color surprisingly fast.  And talk about Polynesian-theme appeal!

 

Randy

[Ralf]

Have you considered a galvanized steel pipe, plugged with epoxy putty at the ends and painted? Considering how much stronger steel is compared to aluminium, one will get away with a smaller diameter and wall thickness. The weight difference will not be that much on a 3.8m length. Price and availability speaks for itself of course.

[Frank Olsen]

Both these Ideas from Randall and Ralph give me an idea.  The Bamboo is appealing as the stern beam.  I like the aesthetics but it would create issues with the front beam that supports the headstay.  I also have never noticed Bamboo that size here in the Pacific NW, not sure how hard it would be to find it.  Changing the headstay to attach to a bridle changes geometry of the jib location.  Placement of a bridle on the Pahi bows would move it aft from the original location, on the beam, which is very far forward and quite elevated on those Polynesian bows.

I had never thought of galvanized but it's definitely worth some analysis!  I now have specs for aluminum from Hanneke so I should be able to find a comparable size in galvanized and see how the weight compares.  Galvanized steel would also allow me to keep my custom made Seagull striker support making less work than creating a new bridle attachment.

Bamboo stern and galvanized bow might be the answer, Thanks Randall and Ralph for the ideas,

Frank

[Randall S Anselmo]

On just a quick Google search, I found http://www.bamboogardenswa.com/poles.html.  I'm sure there are more suppliers to shop from.  I got interested in bamboo while visiting a friend's house in Costa Rica which was framed almost entirely from very sturdy gadua bamboo, joined by lashing.  The 6 to 8 inch diameter poles for his house were grown in a single season! See photos: bamboohousecostarica.blogspot.com

[Marty Peters]

Randall,

Untreated bamboo will loss its colour quite quickly, going from green to grey in less than a week. Leave it in the sun and it goes an unspeaking bleached grey. To help preserve the bamboo and enhance it's beauty, wait until all the green has gone and try taking some dark coloured decking stain and very sparingly apply it only using the very tips of the brush. With a little practise you can apply a very realistic grain effect that really brings out the beauty of bamboo. Adding extra stain around the knuckles makes them stand out. I used this effect on a bamboo fence and it looked great when finished and still looks good 3 years later.

Cheers

Marty

[Frank Olsen]

Having grown up with 3 generations of family in the Pac.  NW lumber and timber industry dealing with Fir Cedar and Hemlock mostly I never imagined bamboo would be a consideration let alone available around here.  I love the idea of bamboo.  Still have some issues to figure out but it's high on my consideration list.

Thanks for the info,

Frank

Randall Anselmo said:

On just a quick Google search, I found http://www.bamboogardenswa.com/poles.html.  I'm sure there are more suppliers to shop from.  I got interested in bamboo while visiting a friend's house in Costa Rica which was framed almost entirely from very sturdy gadua bamboo, joined by lashing.  The 6 to 8 inch diameter poles for his house were grown in a single season! See photos: bamboohousecostarica.blogspot.com

[Randall S Anselmo]

I was looking back, and this is probably the best photo I have, although it was taken before I installed the boarding ladder in the center section.

[Robert Sheridan]

I used an old mast section on my Tiki riged Hinemoa and made holes in the netting large enough for the bridle to pass through without chafing, for the aft netting beam I used the lower section of a laser mast.  I liked being able to stand on the beam in front of the jib.  On our Tiki 30 we used an old boom of a yacht as a aft netting beam and held it on with lashings.  It is pretty easy to pick up old masts and booms from boat yards and riggers  I have found - in the UK at least - that there is no demand for secound hand spars.