Concave bow

[cstay]

So between my stem and frame 18 I have a pretty significant concave section. Did anyone else have this issue and if so how did you fix it?

[Mist]

I wonder how much concave you have and where? I have a little bit on the side panels and none on the bottom. I just measured 1/8", the deepest point between the stem and frame 18, 2" above the chine. I think it looks fair. Should I be concerned?

[Chad]

Hollow up at the shear? Didn't "fix" it, it's the same both sides, so I say it's supposed to be there:

https://picasaweb.google.com/m/zoom?una ... Height=268

[Chad]

I wonder how much concave you have and where? I have a little bit on the side panels and none on the bottom. I just measured 1/8", the deepest point between the stem and frame 18, 2" above the chine. I think it looks fair. Should I be concerned?

Put a 4 or 6' batten on it. If it won't follow the curve, it needs to be fixed or faired.

[Mist]

Funny, my shear doesn't go hollow at all, straight then convex. Seams we should have similar hull shapes. I think I'll leave the hollow at the chine alone.

[cstay]

The shape is ok. It seems the bow stem angle is to steep. What I am worried about is the rules stating that the hull may not be concave.

[ryderp]

My panels definitely have concave sections in front of frame 18 but they are symmetrical (and look pretty good) so I'm not going to worry about it. I do think that the concave sections that people see is due to cutting the bow-stem according to the plans. It would be a really nice service if someone (e.g. Watershed) sold bow-stems that were CNC cut to an ideal shape. Too late for those of us who did it on their own, but for future builders it would be great.

Phil

[Chad]

.... I do think that the concave sections that people see is due to cutting the bow-stem according to the plans.....

I think my build argues against the stem angles being responsible for any concavity. I put my stem in last, and used full length shear and mid-panel stringers, so the concavity is the result of a fair curve as it meets the stem, and can't have been caused by the stem bevels in my case.

The shape is ok. It seems the bow stem angle is to steep. What I am worried about is the rules stating that the hull may not be concave.

Don't think any rules say "no concavity", just not more than X concave than the "design shape". Pretty hard to argue that a fair curve through the design points isnt the design shape, so I don't think there is any need to worry about that.

[cstay]

Awesome! Now I can get to work on frame 18 and the. Drill a big hole for my sprit! What dia carbon sprit is norm 2"?

[jray]

The od of mine is approximately 2 3/4" and it tapers down slightly going forward, which helps with extending and retraction. The sleeve that is fixed to the boat has a od of around 2 7/8" I believe all the C-tech prods are similar. I opted to lash a block to the outside for the tack so there is a little extra reinforcement on mine in that area. Some of the others brought their tack line internally.

[Kevin]

My bow definitely has some concave curve in it. I shaped the stem piece to fit the side panels after stitching all the other frames in. I found that the 20 degree angle on the stem piece was too much, it would have bowed the side panels out more than needed to hit frame 18 with a fair curve.

On the Prod, this is what c-tech spec'ed for an internal prod.
- Prod - 63.5mm ID x 3mm wall tapered laminate @ 2m long. Don't know how "tapered" or where the taper is. The tip is wrapped in twill cloth for strength and fits in the sleeve. I ran my tack internal and fitted a disc of g10 to the end of my tube.
- Sleeve - 70mm ID x 1.2mm wall @ .5m long.
- Bonus outer sleeve - 90mm ID x .9mm wall @ 2.4m long ( connects frame 18 to 110 so that any water that enters the prod runs out into the cockpit and not into the boat. )

As for cutting the holes for the sleeve, the best method I know was Jeff's. cut the hole in 18, then used a light positioned where the aft end of the prod would be and traced that outline onto the hull side panel. My method resulted in a lot more silica filler. The trick is to angle it so the tip is at deck level and on center when extended. I used a string jig to find that point in space personally and then trail and error until I hit the mark.

Kevin

[cstay]

I am going to do a version of what the Pdx guys did with an articulating sprit but I will be using harken track vs the system they had.