Announcements
New Discussions
Previous Thread
Next Thread
Print Thread
Rate Thread
Hop To
Centreboards #64737
01/15/06 10:18 PM
01/15/06 10:18 PM
Joined: Mar 2003
Posts: 943
East Gippsland, Australia
Tim_Mozzie Offline OP
old hand
Tim_Mozzie  Offline OP
old hand

Joined: Mar 2003
Posts: 943
East Gippsland, Australia
Reprint of old Mosquito forum topic:

Peter Foulsum
6/4/05
"Out of the Blue"

Quote
I am about to embark on constructing some new centreboards for the old Mozzie so that it can go faster (The old ones are big, long, heavy and I know that one is warped). The class restrictions are pretty basic which gives alot of scope to do whatever you want with length, width below the maximum limits provided.
I also hope to use the free fore/aft space in the cases to rake the boards backwards. Is there anyone who has experimented with length and width and what is the optimum for both ? The latest foils appear to be 10" wide and approx 1050 mm long. Has anyone used shorter lengths or widths to their advantage. How much can I play around with rake in the case without affecting centre of effort or if it does provide lee helm how much mast rake can be used without affecting downwind performance ? What timbers are best ?



Tim Shepperd
7/4/05
"Karma Cat"

Quote
Hi Peter
Be careful not to overlook rule 5.11 - "The leading and trailing edges of the centreboard slots shall be parallel and within 10degrees of the perpendicular from a straight line along the tops of the main and rear beams."
This means you can't pack the bottom of the case to allow the centreboards to pivot fore-and-aft. You can however achieve the same effect by tapering the top of the centreboards like this:


[Linked Image]


Peter Cobden
8/4/05
"Try Again"

Quote
You will need to read a couple of places in the rules 8.1 through 8.4 along with 5.11. The way the South Australians measure the 10 Degrees angle is by putting the Center Board in the case and measuring the angle from the deck. This measuring method will stop you from doing what you propose unless the method of measuring changes. Center Boards are the place many people have played with and most have end up with what we are using now. I was sailing a Boga this year in light winds and with the kite up we could get the boat to sail sideways through the water to the point that sitting on the boat we could see it. The problem I can see with smaller boards is that in light winds they may not be enough. If you change the boards please keep us informed.

Peter



Peter Foulsum
19/5/05
"Out of the Blue"

Quote
To Peter Cobden. Was it your Mozzie with the 8" centreboards at Loch Sport ?


Peter Cobden
13/6/05
"Try Again"

Quote
Peter,
Not my boat, it has 11" centre boards. Most of the new boats we built have 10" centre boards. I know one person is using Jim Boyers new 9" A-Class boards and one other boat has Tony McKenzie 9" boards.
As for 8" boards I don't know who is using them.
Peter


Peter Foulsum
21/6/05
"Out of the Blue"

Quote
Discovered that the leading edge rake angle on my Mossie is 5 degrees. This gives me another 5 degrees of rake that I didn't previously consider. Hope to make up some fibreglassed foam guides and install them in the case slot. This should provide the additional centreboard rake I'm looking for and give me some scope for raking the mast back. Those with older mossies should also check their case rake angles.



Peter Foulsum
23/10/05
"Out of the Blue"

Quote
After much consternation finally bit the bullet and fitted the fibreglassed foam wedges 17/10, 18/10 and 20/10.

Saturday morning 22/10 9:00 am started cutting and fitting rubber strips to the fore and aft faces of the new slots. 11:00 am started cutting the aft sections off the existing centreboards with a hand saw. 12:10 pm applied Everdure primer to the exposed bare timber and set aside to dry. 1:00 pm had Mozzie on the beach for opening day race.

1st impressions: feels faster with slight lee helm. Will eventually adjust mast rake to suit. Now have to fill the gaping cavity at the leading edges left by the inserted wedges (not quite long enough). I have plenty of foam left over so will model some this week and glue it in place next Satuday morning and see if there is further improvement. Also need to feather the trailing edges of my modified centreboards.



Peter Foulsum
19/12/05
"Out of the Blue"

Quote
Thought I should finally put this to rest. Revised centreboard cases and centreboards have made an enormous difference to boat speed and handling. Now have no vibrations from centreboards at high speed and reaching with centreboards fully down is a dream compared to the old design. Am now able to keep the other newer Mozzies honest even with the ancient sail that I keep persevering with. So to those of you with old Mozzies kicking around I would strongly advise the change.

Regards,

Peter Foulsum
p.s. Finished 2nd on Yardstick and 2nd on Handicap in club pre-christmas series. Maybe it was because others broke stuff capsized or didn't turn up.



Attached Files
65075-20centreboards.jpg (227 downloads)
Last edited by Tim_Mozzie; 01/15/06 10:21 PM.

Tim Shepperd
Mosquito 1775
Karma Cat
-- Have You Seen This? --
Re: Centreboards [Re: Tim_Mozzie] #64738
09/03/06 06:04 AM
09/03/06 06:04 AM
Joined: Jun 2006
Posts: 265
Sydney AUST
becjm Offline
enthusiast
becjm  Offline
enthusiast

Joined: Jun 2006
Posts: 265
Sydney AUST
I am looking at making some new centerboards mine are old,bulky& falling appart.Anyone have any tips and maybee any photos. I feel i could pick up some speed with better designed boards.

BEN 654


---Ben Cutmore---
--MOSQUITO 1704--
Re: Centreboards [Re: becjm] #64739
09/03/06 07:34 AM
09/03/06 07:34 AM
Joined: Oct 2005
Posts: 951
Brisbane, Queensland, Australi...
ncik Offline
old hand
ncik  Offline
old hand

Joined: Oct 2005
Posts: 951
Brisbane, Queensland, Australi...
I have just made some rudders and offer the following method, there are other ways.

1. laminate together some good quality (no knots) western red cedar
2. plane section of board that is in the water to roughly a naca 00xx section with blunt trailing and leading edges, leave top section square cause it's in the case
3. apply epoxy and microfibre bead to leading and trailing edges (it's tougher than timber and will handle dints better)
4. shape board to more closely resemble the desired section shape (naca 00xx) making sure to leave about 5mm of hard epoxy at the leading a trailing edges, sharp at trailing edge, elliptical at leading edge. finish should be sanded, not planed
5. cut board profile to desired and class legal shape, fine tune bottom and corners with sanding
6. apply a layer of 120-160 gsm fibreglass woven mat (not chopped strand) with epoxy (not polyester). the glass should wrap around the front and finish well behind the trailing edge. do not make it too wet, should be able to use an old credit card to squeegee the resin around evenly and get rid of excess, but don't leave it too dry. if you know how to use peel ply, that is preferred method over squeegee.
7. trim glass off roughly and give a light sand all over
8. apply an adequate coat of bog (epoxy and microballoons or similar)
9. fair with a small torture board only (an mdf board with sandpaper attached about 1 foot long, 5-10cm wide, cut a sanding block in half and glue on top for handles) fair to, but not through, the layer of glass
10. if needed, keep applying bog until happy with fairness (in my opinion, fairness is much more important than section shape) final touch-up fair can be done much quicker with car bog from any hardware store
11. paint with 2-pack primer and 2-pack gloss (don't waste time with the single packs for boards, the new teflon paints are too soft and get shredded in the centreboard case, probably best to get a professional to do the actual painting, the fumes off 2-packs are really bad, I felt off for over a month afterwards, I didn't buy a gas mask that was suited to the paint but thought close enough was good enough, read the label)

notes:
- if you intend to put holes or fittings in the board, make hard points for them with a modified epoxy and microfibre before apply the glass.
- get good dust masks and keep them clean, western red cedar dust isn't good for the lungs. good quality, proper fitting, dual elastic band disposables are fine. don't waste time with the cheap and nasty single banded ones, I've blown black snot (excuse the language) for a week after sanding carbon with one of those on!!! Not good...
- I hope I haven't scared you off it, if you give yourself enough time and take the proper precautions, you should be fine. With all boat work, attention to detail is important.

As you can see, there is a fair bit of work involved in making new blades to a semi-professional standard. I enjoy doing my own because I'm sadistic. I would certainly repair my boards in the future, but probably not make from scratch again, unless I could female mould them.

I much prefer sailing over building.

Re: Centreboards [Re: ncik] #64740
09/03/06 01:47 PM
09/03/06 01:47 PM
Joined: May 2003
Posts: 4,451
West coast of Norway
Rolf_Nilsen Offline
Carpal Tunnel
Rolf_Nilsen  Offline
Carpal Tunnel

Joined: May 2003
Posts: 4,451
West coast of Norway
Just a small comment on fairness vs. section shape.

Fairness, a smooth surface and sectional shape are all very important. When NASA tests sections, they are shaped to 1/1000 of an inch. Then theorethical and practical results start to match. Laminar sections are more demanding than the NACA 00xx series.

Re: Centreboards [Re: Rolf_Nilsen] #64741
09/03/06 08:14 PM
09/03/06 08:14 PM
Joined: Oct 2005
Posts: 951
Brisbane, Queensland, Australi...
ncik Offline
old hand
ncik  Offline
old hand

Joined: Oct 2005
Posts: 951
Brisbane, Queensland, Australi...
What do you mean by "demanding"...to build? If there is any concavity in the sections they will be very demanding to build.

I think the accuracy limit of a home builder in terms of section shape would only be in the order of 0.5mm, even 1mm deviations from the exact shape wouldn't be uncommon I suspect. It's difficult to achieve close to exact shapes without a very expensive construction method, which would be beyond most home builders.

On the other hand, it is very easy to achieve close to perfect fairness with patience and attention to detail.

What I'm trying to say is try and get the section shape close but don't be too pedantic with it, spend more of your time fairing as perfectly as you can with a good torture board.

Last edited by nickb; 09/03/06 08:18 PM.
Re: Centreboards [Re: ncik] #64742
09/04/06 01:37 AM
09/04/06 01:37 AM
Joined: May 2003
Posts: 4,451
West coast of Norway
Rolf_Nilsen Offline
Carpal Tunnel
Rolf_Nilsen  Offline
Carpal Tunnel

Joined: May 2003
Posts: 4,451
West coast of Norway
I meant to say that the need for accuracy is even higher for the laminar flow sections as compared to non-laminar sections. So it makes them harder to build, yes. Unless you have access to a CNC mill. Point I am trying to stress is that hand building foils to a sectional shape like e.g. the NACA series is very hard if you are aiming at a concrete set of properties in the finished product.
Getting down to 0.5mm with a hand plane and belt sander, while keeping the foil straight lengthwise, is pretty well done in my experience. I tried my hand at a couple of ply/glass foils some time ago, and it was tedious work ending in a not too good result. I liked Phill Branders method better, where he made a outline of the section he wanted and glued sandpaper to it. Then proceeded shaping foam with this "jig", before laminating carbon to it and glueing the halves together. He used to have some photos of the process on his website (which have disappeared due to changes the web provider did).

Re: Centreboards [Re: Rolf_Nilsen] #64743
09/04/06 02:53 AM
09/04/06 02:53 AM
Joined: Oct 2005
Posts: 951
Brisbane, Queensland, Australi...
ncik Offline
old hand
ncik  Offline
old hand

Joined: Oct 2005
Posts: 951
Brisbane, Queensland, Australi...
I forgot to mention that an alternative to strip planked western red cedar is to just use some exterior ply, shape and glass.

I like the idea of shaping foam then adding carbon, might try that sometime.

The moths are making their hydrofoils with mdf female moulds. If interested the forum Moth Forum would be a good place to start research. Probably not a bad alternative.

Re: Centreboards [Re: Tim_Mozzie] #64744
09/04/06 03:20 AM
09/04/06 03:20 AM
Joined: Jan 2006
Posts: 29
S
soggy Offline
newbie
soggy  Offline
newbie
S

Joined: Jan 2006
Posts: 29
Is this the "Phil Brander" article you refer to ??

Paul
canberra

Re: Centreboards [Re: soggy] #64745
09/04/06 05:59 AM
09/04/06 05:59 AM
Joined: Jun 2006
Posts: 265
Sydney AUST
becjm Offline
enthusiast
becjm  Offline
enthusiast

Joined: Jun 2006
Posts: 265
Sydney AUST
Thanks for those tips on makeing the centerboards.My frend plays allot with carbon fibre & is in the process of purchacing a special vacume bag table.(all i know is that its quite an expensive table)Any comments on width and length? I would like them not to pretrude thru the hulls when they are pulled up but this would mean that the length in the down position thru the hulls would be only 500mm.They are currently 300mm wide& about 1200mm long.


---Ben Cutmore---
--MOSQUITO 1704--
Re: Centreboards [Re: becjm] #64746
09/04/06 07:30 AM
09/04/06 07:30 AM
Joined: Jan 2006
Posts: 556
Somers, Westernport Bay, Victo...
Peter_Foulsum Offline
addict
Peter_Foulsum  Offline
addict

Joined: Jan 2006
Posts: 556
Somers, Westernport Bay, Victo...
Mine are now 250 mm wide and 1020 long and I haven't looked back since I cut them down (less drag and same pointing ability). Just make sure that you keep the trailing edge of the case where it is and build up the front edge of the case to suit.


Mosquito 1814
Macka Mozzie
Re: Centreboards [Re: Peter_Foulsum] #64747
09/05/06 12:11 AM
09/05/06 12:11 AM
Joined: Jan 2006
Posts: 29
S
soggy Offline
newbie
soggy  Offline
newbie
S

Joined: Jan 2006
Posts: 29
Think I have found the article on vacuum bagging by Phil.

http://au.pg.photos.yahoo.com/ph/phillbrander/my_photos

Also a some information available on vacuum bagging from the model aircraft folk.

http://home.paonline.com/hayman/PAGE2.htm

Paul
Canberra

Re: Centreboards [Re: soggy] #64748
09/05/06 01:39 AM
09/05/06 01:39 AM
Joined: Mar 2006
Posts: 97
Adelaide, Australia
Tony_Snape Offline
journeyman
Tony_Snape  Offline
journeyman

Joined: Mar 2006
Posts: 97
Adelaide, Australia
I haven't read this whole post but do have experience in vacuum bagging advanced composites during my airforce career. There are some accessories like vacuum valves and nylon bagging film etc, available through these guys that will make your life a lot easier.

Advanced Composites
21 Waverley Drive
Unandurra NSW
02 4272 3200

Cheers


Tony Mosquito 1743 'Phat Cat'
Re: Centreboards [Re: Tony_Snape] #64749
09/05/06 02:25 AM
09/05/06 02:25 AM
Joined: Oct 2005
Posts: 951
Brisbane, Queensland, Australi...
ncik Offline
old hand
ncik  Offline
old hand

Joined: Oct 2005
Posts: 951
Brisbane, Queensland, Australi...
I have seen bubble wrap used very effectively for vacuum bagging on a table. Neither peel ply nor absorption material was required, however it was a fairly industrial application. Probably better to test it on a practice item before anything good.

Re: Centreboards [Re: ncik] #64750
09/07/06 06:34 PM
09/07/06 06:34 PM
Joined: Jun 2001
Posts: 1,449
P
phill Offline
veteran
phill  Offline
veteran
P

Joined: Jun 2001
Posts: 1,449
I think you're better off using peel ply and an absorption material that is layed flat with no creases.
(Crease the peel ply, absorption material or the vacuum film for that matter and it will show up in the surface of the laminate.)
I think the method I used will give you the lightest strongest and truest board.
Taking care with the peel ply,absorption material and vacuum film will minimise the finishing you may have to do.

To make a board lighter and stronger you would probably have to go to a near hollow board with pre-preg carbon.


I know that the voices in my head aint real,
but they have some pretty good ideas.
There is no such thing as a quick fix and I've never had free lunch!


Moderated by  Damon Linkous 

Search

Who's Online Now
0 registered members (), 625 guests, and 166 spiders.
Key: Admin, Global Mod, Mod
Newest Members
Darryl, zorro, CraigJ, PaulEddo2, AUS180
8150 Registered Users
Top Posters(30 Days)
Forum Statistics
Forums26
Topics22,404
Posts267,055
Members8,150
Most Online2,167
Dec 19th, 2022
--Advertisement--
Powered by UBB.threads™ PHP Forum Software 7.7.1