Thoughts on Appropriate Material Please

[BrianR]

I'm strip building the Melonseed (13 foot version). The outside of my hull is done, faired, glassed with 6 oz., and coated with epoxy.

Now, I'm going to fair and coat the inside. I've read good things about Xynole, and Kevlar. If I can, I'm going to build this without ribs. Of course, the Kevlar is 18 bucks a yard, and both Xynole and glass are much cheaper.

My strips are about 3/16 inches thick.

Is it worth it for me use the Kevlar, or should I stick with Xynole or glass?

Thanks in advance everyone.

[ 08-18-2004, 12:08 PM: Message edited by: BrianR ]

[mmd]

I would go for the xynole or 'glass for the simple reason that if you have to do repairs to the interior (you almost definitely will, at some time) kevlar is a monster to repair cleanly. It just won't sand down smooth. Also, the advantages of kevlar (tensile strength) are not needed in this application unless you plan on running the Grand Canyon in flood season. ;)

[Popeye]

Kevlar and exotics are selected for special applications for example weight/strength , and typically cost would not be considered.

Do you need a Ferrarri to pick up groceries?

[Bill Perkins]

Brian xynole doesn't wet out clear , if that's important to you . It also soaks up allot more resin than 6 oz. cloth .

[ 08-18-2004, 01:15 PM: Message edited by: Bill Perkins ]

[Keith Wilson]

Kevlar is wildly expensive, has superb tensile strength for its weight and is a pain in the posterior in every other respect, or so I've been told - I have never used it myself. For this application, particularly inboard, I wouldn't bother.

Glass has good tensile strength and moderate abrasion resistance, is fairly cheap and readily available almost everytwhere, and is not too hard to work with. Xynole has excellent abrasion resistance and only moderate tensile strengh, and is harder to work with because it floats up in the resin and sands fuzzy. I'd use glass.

[JimConlin]

I would be concerned that on such thin planking the xynole, being stretchier than glass would give you an inadequately stiff panel.
Is there an engineer in the house who can calculate the stiffness of the glass/core/xynole panel?
I'd make a 2'x2' panel and beat it up.

[ 08-18-2004, 01:27 PM: Message edited by: JimConlin ]

[Chadd Hamilton]

Brian, let's see some pictures of the 'seed!

Chadd

[paladin]

if you done built the boat rite....it's strong enough without anything else.......kevlar is placed on the INSIDE of a hull for impact resistance...it reduces the tendency of the hull to splinter inward and puncture as the kevlar stretches a bit before separating.....Xynole is used purely for abrasion resistance on the outside of the hull and to protect the wood...use care in the manner that you select the epoxy that you use....a "thinner" epoxy like MAS will wet out the fabric better.....I have three layers of Xynole on my boat to about 4 inches above the LWL and two to the gunnel and the rest of the boat...had minor scrapes but no wood damage yet...(knock on WOOD)

[George Roberts]

BrianR ---

Who suggested 3/16" strips and 6oz glass? And what did the plans call for?

Just looking at the boats dimensions I think you made a mistake.

I don't think it matters about what you do with the inside unless you add some material to the outside.

[John Meachen]

I don't know that Kevlar for reinforcing hulls would be practical.The fuzziness that it suffers when cut or abraded is bad enough but potentially worse is the degradation it suffers in UV light.I have first hand experience of several main halyards breaking after a few weeks exposure to sunlight.Will your paint be a better barrier than the sheathing on the rope?

[BrianR]

George! I sure hope you are wrong! The strips were cut to 1/4 originally, but I'm thinking that after the fairing, they're down to 3/16 inches now. On top of the glass, I've got three or four coats of epoxy. Sure hope that, combined with the glass inside, is enough. If you still think I'm wrong - please elaborate as to your reasons!

To everyone else - thanks for your thoughts. I'll stick with the glass.

To Chad:

Lets see if this works:

http://www.imagestation.com/picture/sraid136/p0ed0e8cdd6f454fcfef1921081977a61/f75e534c.jpg

http://www.imagestation.com/picture/sraid136/pc09a78fa536ca2f9cacee138b75d74f7/f75e5343.jpg

http://www.imagestation.com/picture/sraid136/pdd43798c08c709bf85f0ff9023566f93/f75e532e.jpg

http://www.imagestation.com/picture/sraid136/p2cb13769867f82eb297a88b2e63c6f6f/f75e5323.jpg

[ 08-18-2004, 07:02 PM: Message edited by: BrianR ]

[George Roberts]

BrianR ---

First, extra layers of epoxy add no strength.

Second, I asked what the plans called for.

Finally, many people who use much smaller boats like kayaks and canoes find 1/4" wood strips and 6oz of glass to be less than desirable.

[BrianR]

Thanks George. The plans don't specify when using the stip/epoxy method. They contemplate 6 mm okoume ply.

What is your thought on how best to increase my strength at this point?

Thanks.

[sangraal]

Hello all,
I'm a new member here, but have viewed and learned alot here. I've built a few canoes and kayaks, dinghy's and am finishing an acorn skiff. And, like all the rest of you i wake up and go to sleep with boats on the brain, with some exceptions of course! hope to spawn many more 'til my final breath!
You might consider using one layer of 5.8oz S-glass over your 6 oz. ext'r if your looking to stiffen the hull w/o frames. and then the same schedule inside- 1 6oz E,1 6 oz'S' final layer. the thing is to maintain a balanced laminate on both sides of your core strips. and using your stiffest fabric on the outside gets them farther from the center/nuetral axis = more overall stiffness. 'E' is roughly 30%
stronger tensile and 15% stiffer than E-glass-std F/G. also more durable.Kevlar needs $$$ scissors too just to cut it. Kev is great for Boundray Waters Boats, etc, otherwise not worth the trouble.
E-glass is available in 6 oz. from Wicks Aircraft Supply, Aircraft Spruce and Specialty,or other glass shops as you can find. I've also seen it in lighter wts in a model airplane suppliers catalog- some company in Tehachipie,Ca. It's a bit pricey,$16 per yd=15 sq.ft.(60" wide)for the 6oz, so you'll need to weigh the pro's and cons- cost/wt of more glass/epoxy/sanding vs. wt/time to fab and install frames, the interior clutter/ added refinishing time at next paint/varnish . the plus of frames is they look the great IMHO.
also 1/4 strips should be fine. i built my first canoe with 7/32 d.fir and 4 oz glass after talking to the tech guy at gougeon's. saved some wt. It holds up great 13 years later, some may not like the flex in the bottom, so build it heavier. if your easy on it you save wt. if you want a beater build it heavy. you decide.no hard and fast rules!
BTW,your pics look great, nice project choice!
And if this is your first boat your doing good work and your in for a real Inner reward/treat at launch time The Gratification!........
take care

[paladin]

VERY nice work.......