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Re: Strip: Petrel: External Stems
By:Bill Hamm
Date: 11/1/2009, 12:21 am
In Response To: Strip: Petrel: External Stems (Jim Flowers)

: I followed the CLC pattern for the internal stems and wound up with fairly
: fine ends. I think I read somewhere that external stems are now favored
: for the Petrel design. Unfortunately, there is no information, pattern or
: material in the CLC kit and nothing Petrel-specific in Nick's book or
: posted in the forum regarding size or shape of external stems.

: From reading various posts it looks like I should trim the strip ends back to
: the 1/2" width and then laminate the stems from 3 strips of 3mm ash
: tapered to a 5mm radius at the outer edge.

: Some questions remain, however.

: 1. I noticed some references to mortising the external stem through to the
: internal stem. Does this serve some hidden (to me) purpose when the
: strength comes from the fiberglass, anyway or should I just skip it?
: Without a mortising bit, I would have to do this with drill and chisel so
: why not just use a dowel?

: 2. Is it particularly advantageous to glass the hull before adding the
: external stems and then glassing them over separately or is it just as
: acceptable to affix the stems before any glassing?

: 3. How far back should the stems follow the relatively flat keel? One post
: suggested about 10", in general, and that looks about right for the
: Petrel lines. A somewhat heartier external stem for the stern is suggested
: to provide better tracking but as this is to be used as a play boat, I
: don't see the need for that.

: Still trying to catch up.

First, on any design I feel an external stem isn't required, adding a layer of glass or for that matter a couple layers would make it just as strong and would be easier to do. I though think an external stem is pretty, specially if you use contrasting woods in the alternate layers. On my Disko Bay I used 5 layers total of white ash and honduras mahogany. I also sanded back the edges of the strips so the external stem would be laminated to the internal stem, but that's gross overkill. On where to end it; it's kinda up to the builder, whatever looks right to you. When I built the DB I'd planned to add a graphite bottom at some point so wanted the external stems to stop before they'd be painted black. They are fairly rugged and will take a fair amount of punishment and the ends of the boat take more abuse usually so that's one thing to think about. Downside is, it's hardwood so any extra length adds weight.

Bill H.

Messages In This Thread

Strip: Petrel: External Stems
Jim Flowers -- 10/31/2009, 11:34 pm
Re: Strip: Petrel: External Stems - Laminate?
Jim Flowers -- 11/3/2009, 2:05 am
Re: Strip: Petrel: External Stems - Laminate?
Bill Hamm -- 11/4/2009, 1:53 am
Re: Strip: Petrel: External Stems
Bill Hamm -- 11/1/2009, 12:21 am
Re: Strip: Petrel: External Stems
george jung -- 11/1/2009, 8:49 pm
Re: Strip: Petrel: External Stems
Allan -- 11/1/2009, 12:18 am