Hobie Forums
http://www.hobie.com/au/en/forums/

Daggerboard / Hull fit
http://www.hobie.com/au/en/forums/viewtopic.php?f=13&t=36729		 Page 1 of 1
Author:  rehmbo [ Tue Jul 12, 2011 1:15 pm ]
Post subject:  Daggerboard / Hull fit
When we're on a cookin' reach on a starboard tack, water starts coming up through the lee (port) daggerboard well. The hull itself takes on no water, so its not a leak issue. I presume its related to proper fit between daggerboard and trunk at the bottom of the hull. Starboard hull doesn't do this.

Question is: What is the best method/material to fix this? I read somewhere about possibly attaching the fuzzy side of self-adhesive velcro around the inner surface near the opening to help shim it in, but not sure... Ideas guys??
Author:  divimon2000 [ Fri Jul 15, 2011 12:40 pm ]
Post subject:  Re: Daggerboard / Hull fit
Never had this problem (or never noticed it!), but in the old Chrysler Buccaneer we used to sail, we used a strip of mylar 5200'd to the bottom of the opening to cover the opening completely, the mylar had a slit in it for the centerboard and was flexible enough to let the board thru and not much else in (water).
Author:  presto13031 [ Fri Jul 15, 2011 1:15 pm ]
Post subject:  Re: Daggerboard / Hull fit
Physics.
Get a glass of water and a straw. Blow across the end of the straw like you would a beer bottle and the water will rise in the straw due to the pressure drop at the top. What is happening in the dagger board trunk is the pressure in the water is rising relative to the air inside causing the same phenomenon.

If the boat is floating stationary, with the board out, the water line on the outside of the hull and the inside of the well will be the same. As speed increases two things will happen:

1) The stationary water will "pile" up at the rear of the moving well.

2) The daggerboard well draws the water into the well due to lower hydrostatic pressure in the well. The combination of both of these will cause the water to flow up and out of the well.
Author:  rehmbo [ Sun Jul 17, 2011 5:34 am ]
Post subject:  Re: Daggerboard / Hull fit
Thanks Presto. I too sat through a couple semesters of fluid dynamics. Bernoulli was my good friend (or perhaps not!! :roll: ) I knew the why, but was looking for advice on the best method to correct it.

Based on some inspiration from Centmichsailor's project, I decided to move forward.

I originally had about 1/4" lateral movement of the boards in both trunks. Looking down the trunk well with the board in place, the 1/8" gap on each side was clearly visible. Here's a pick looking from the bottom side before correcting.
Image

I considered both closed-cell vinyl foam (3mm = ~1/8") and the fuzzy side of the Velcro (3M/Scotch RF7760; comes in white or black; 15' roll was about $5). I got them at Menards, but any hardware store should carry it. I was afraid the higher friction of the vinyl/rubber might cause board insertion/removal issues or get peeled off by the board, so I went with the velcro (fuzzy side).

I cut it into strips about 90% the length of the trunk. Application was tricky as the adhesive is very sticky/tenacious, and getting both the proper distance from the bottom (I decided on about 1/8") and the correct angle were a challenge.

Board fit is now "perfect" - its still easy to insert/remove, with a nice snug fit with no lateral movement and very little area for water to come up. Unfortunately no wind is forecasted this weekend, so I can't test it...

Only potential issue with the tighter fit that I can imagine is that it might induce some drag if the overall boat has any toe-in/out issues. Last time I measured the hull, it was within 1/8" on flat water, but I'll probably be more conscientious about raising the windward board when sailing flat.

Here are a few photos after the fix.

Image
Looking down the trunk

Image
Bottom view board-out

Image
Bottom - board-in

I placed 4 pieces each just below the top edge of the trunk at front/rear and sides similar to centmichsailors project. This should prevent excess movement at the top and help limit some abrasion seen in this area.

Hope this is helpful. I'll let you know how things go...
Author:  MBounds [ Sun Jul 17, 2011 6:07 pm ]
Post subject:  Re: Daggerboard / Hull fit
Be very careful about letting sand, or worse - small pebbles - get into that setup.
Author:  presto13031 [ Sun Jul 17, 2011 7:30 pm ]
Post subject:  Re: Daggerboard / Hull fit
Mine do it too I just live with it :D too lazy to fix it
Author:  rehmbo [ Wed Jul 20, 2011 12:14 pm ]
Post subject:  Re: Daggerboard / Hull fit
Thanks Matt. Roger that.

Sand/pebbles shouldn't be an issue at my home lake, but will be triply careful on any beach launches.

Racing this weekend with CRAM at Caseville. Hope there is enough wind to give it the final thumbs-up or thumbs-down conclusion.
Author:  LeelanauH18 [ Fri Jul 22, 2011 12:03 pm ]
Post subject:  Re: Daggerboard / Hull fit
I strongly echo Matt's warnings about sand and pebbles. This past winter I completed an overhaul on my daggerboards to clean up the trailing edges and make them shiny – had them looking nearly new again. (Spraying the gel was a learning experience.) Hoping to protect my “new” boards, I applied some Velcro to each corner of the daggerboard wells – including the bottom ones. Bad decision.

No problems the first few outings of the year, then launched the boat from the beach on a relatively windy day and was confused when I couldn’t get the boards to go down. Getting frustrated (thought it was just lateral pressure) I forced them and they relented… Came in after about an hour, pulled the boards out and to my disgust, the new gel and some of the fiberglass was cracked and flaking along 8 inches of the trailing edges of each board. In trying to figure out what caused it, I pulled the boat up on my hoist, looked underneath and sure enough there were a bunch of small pebbles and sand lodged into the Velcro in the tight aft corners.

So now I get a little more practice with fiberglass and gelcoat come fall. Only took that one hour of sailing for the boards to sustain enough damage to return them to their previous jagged condition from 25 years of abuse. I’ll post some pictures once I'm able. They’re still a little hard for me to look at.
Page 1 of 1 All times are UTC - 8 hours [ DST ]
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/