MartinRF
-
Content Count
364 -
Joined
-
Last visited
-
Days Won
4
Content Type
Profiles
Media Demo
Forums
Gallery
Calendar
Store
Posts posted by MartinRF
-
-
Looks comfortable enough to me. Standing headroom...
/Martin
-
I think Richard left the UK well before 2009 but I may be wrong. He is mostly operating out of British Columbia now.
/Martin
-
Here people are showeling snow from roofs...
/Martin
-
I have 5 hp outboard in the nacelle but I don't use it much. Maybe 3 hours last season.
Yes, strip-planked cat: http://hem.bredband.net/b262106/
From a bicycle commute point of view Stockholm has very few hills. My native Gothenburg on the other hand... Less snow in Gothenburg though. I do have spiked winter tyres on my bicycle in winter. 7.5 km commute.
/Martin
-
A couple of months ago I promised to publish a video showing my sailing grounds. Here it is: https://youtu.be/g2Tt4IvKd5A
Not the most exciting sailing from last season but then I was to busy sailing to dig out the camera.
Some other of my antics recorded on film: commuting to work in snow in November: https://youtu.be/Mmj0my0B07Q
Merry seasonal greetings to all,
/Martin
-
-
Yeah, I thought about that block too. A ball bearing block for a static load does not make much sense to me.
This study may interest you: http://hem.bredband.net/b262106/Boat/Blockfriction.pdf
/Martin
-
Let me start with a disclaimer: I have no first-hand experience of synthetic standing rigging. My all-steel implementation is very similar but with three extra toggles to minimize fatigue inducing bending of the wires.
To me the implementation shown in your photos looks really good. I would replace what is worn without changing anything.
Others may have wiser advice...
/Martin
-
Nice!
Your sailing grounds are very different from mine. I'll post a video showing mine sometime.
Over canvassed is very relative. Single handed sailing I am fully powered up at 10+ knots -- to windward that is. Fully crewed I have a lot more righting moment.
/Martin
-
Good to hear that.
/Martin
-
Or:
I don't kno the guy who posted this but I know the one who made the video.
/Martin
-
Just to show that there is more than one active Tennant cat in the northern hemisphere.
After work sailing this Tuesday testing my new jib and a Sony action cam. Sunset at 22.09...
/Martin
-
Life is hard
/Martin
-
Been there, done that -- because we ignored the manual and used self-tailing winches for the sheets.
Long time ago, 40 ft French former racing cat.
Another very successful French cat, a racers-cruiser was named "inoui" beccause it reads the same upside down. I don't think she has ever capsized. Owned by a family who had built her. Teachers from Bordeaux and very enthusiastic sailors. Sailing to Norway on summer vacation? Sure, why not? Crossing the Atlantic? Absolutely!
Met them in Gonthenburg in the early 1990s.
/Martin
-
My two pence on balance:
If rudders are not contributing to lift they are *only* drag.
Drag vs Lift follows a quadratic curve so adding a little lift (from zero) on the rudders increase their drag slightly while the daggers are operating further up their drag-vs-lift curves and will loose more drag as the rudders start to share the load. This reasoning assumes rudders are reasonably sized and deep.
If the centre of effort of the rudders are on or very close their axle through their pintles there will be very little tiller load and if you are used to a heavy-on-the-tiller mono you may find it hard to 'read' the cat balance from the tillers.
I do not know what prevents your rig from rotating. Bring someone experienced along for a ride.
/Martin
-
He already got the cruising cat, sailed it home from South Africa.
/Martin
-
I think you should try to find out what mast bend and mast characteristics this sail's luff curve is designed for. If it is significantly different from what you can achieve you should factor in a luff curve re-cut.
/Martin
-
Interesting. I have a similar set-up these days but I have to help the car or it will stop too close to the centre-line of the boat. I usually only have to pull it down after a tack and then the car stays in the right place. I higher winds, however, I have to apply the outhaul all the time as I want to open up the slot and still sheet the jib flat and that does not happen of itself with a straight track -- not on my boat at least.
Call it semi-self-tacking...
/Martin
-
The red ball is on the unloaded side of the dagger board case -- where the board isn't even touching the case.
/Martin
-
Photos or it didn't happen
Here is one I created just before bicycling home today:
This is for the floor-less case with the board pushing on the left side of the hull opening. Red arrows show material in tension and blue arrows to the left of the hole shows the material is in compression.
The red 'ball' is just an indicator showing the centre of rotation when I was manipulating the view.
/Martin
-
1
-
-
Here is the 1986 calculations explained in English. This is kind of brief but I hope it makes sense.
I tried to attach the LibreOffice spreadsheet as well but that was not permitted.
It is my current understanding that real composite experts do not design reiforcements looking like this but it may still be the best option for paxfish. (The presence of the floor calls for a modification in the laminate scheme though.)
One thing not addressed here is how to avoid locally crunching the hull laminate.
/Martin
-
It is easy to impress by using computer generated graphics
I think it does a good job of illustrating where potential problem areas are. Unfortunately it does not offer a way forward to determining proper laminates. The reason is I don't have tools for modelling composites - I have used homogenous, isotropic materials and composites are layered and orthotropic. What I miss is something like this:
It is possibe to make do without this helper add-on by 'drawing' the layers and creating the local coordinate systems manuallly but it would be very time consuming.
But all hope is not lost. Back in 1986 I engneered both boards and hull reinforcements using pen, paper and pocket calculator(*). I actually found my notes the other day and have scanned them for your enjoyment.
Structural_engineering_of_daggerboards_in_1986.pdf
The engineering assumptions are crude but they worked. The boat is 30 years old and we have had no problems with boards or hulls. The original boards where all glass/epoxy and weighed 15 kg a piece. I built deeper and slightly thinner boards in 1995. Using carbon in the main spar of the boards the new ones weighs 13 kg a piece.
I still stick to the same basic engineering principles with few improvements related to better understanding of fatigue limits of composites. See http://hem.bredband.net/b262106/Boat/dagger.html and the documents linked to this page.
I will try to write an explaination to the hull exit reinforcement engineering of 1986 asap, maybe this weekend. It isn't exactly 'rocket science' so it shouldn't be too hard to grasp.
/Martin
*) Martyn Smith once told me he used those tools and no other to engineer the composite structure of Formule TAG.
-
-
No FEA results yet but I have created an illustration to show the importance of having a healthy separation between upper and lower (boat bottom) supports for the dagger board:
Figures are from my boat and the support separation in the drawings we bought is roughly 20 cm! The Wildfire design looks better in this respect but I think I would prefer even more separation in the interest of reducing material stress.
/Martin
PS Only using free and open software this time: LibreOffice on a Linux system.
go force to fiji in 3 days
in MarineTalk
Posted
Same as my boat then.
Reefing early helps. You don't have to sail the boat to its potential.
/Martin