Extend Rudders on 10metre sailing catamaran

[TomBlake]

some photos. Not alot of bridge deck clearance. Haven't taken it out too far as yet. We've been sailing around Moreton Bay and the channels down to the Gold coast (Queensland, Australia) Need to sort out rudders and stern rail/davit first

 

[fallguy]

Looks like plenty of deck clearance for 10m cat to me. Perhaps it is an illusion.

 

[tspeer]

See photo. When fully down rudders already rake forward quite abitView attachment 157703

Yes, that's exactly my point.

Try sailing with them raked less forward, and see if the boat still wanders. If it acts more stably, then your problem is over-balanced rudders, not a lack of rudder area.

If you do make them longer, don't just continue with the same rake angle. You have plenty of area ahead of the steering axis as it is. You should extend the rudder straight downward, or even rake the extension back a bit.

 

[TomBlake]

Thanks. I'll try that. The mechanism is abit primitive to adjust. At the moment you have to cleat off the rope which pulls the rudders up. Not good if I hit something there is no give. Can anyone suggest a way of locking the rudders in place once I have them balanced. I have purchased a couple of release cleats

The previous owner screwed or glued cleat and block fittings onto the deck!! Not bolted through. And his mates said he was very fastidious!!???

 

[catsketcher]

Gday Tom

A couple of points.

I don't like to do anything but agree with Tom as he is very clever, but I would think that if the rudders themselves are wandering, then you have overbalance. If you let go of the rudder and it wants to follow the boat nicely, then the rudders are not overbalanced. With the extra shots of your boat, I would be pretty certain you will be pulling those rudders out of the water in a Moreton Bay chop. I have only sailed one boat with over balance and I had to actually concentrate on keeping the rudder central, it was quite hard to do and very obvious.

You should put some stops in the rudder boxes to stop the rudders when they reach the correct position. A small piece of timber glued in the right spot and smothered in epoxy would work.

As for the hold down lines - this is pretty common. You can use a special cleat like below

Clamcleat ® CL257 Auto Release Cleat for Rudders | Coast Water Sports https://www.coastwatersports.com/clamcleat-cl257-auto-release-cleat-for-rudders-p-3471.html?currency=AUD&gclid=Cj0KCQjwirz3BRD_ARIsAImf7LM8lVC0ftXFw_gtY3g85eswhbcN0BYV3jjlMwhNoDzFpnNK3a-JcSkaAjW6EALw_wcB

Or you can include a fuse of thin VB cord at the start of the line. This will break if you hit the ground.

In reality, you rarely hit the ground fast. What you may do is run over a fishing float. With your centreboards you could tangle in them. I always have my boards up running deep and have only tagged a fishing float on the centreboards once and that was a pain. I would go for the special cleat as you can then go to the stern and pull the rudder down again. I have popped the rudders about 12 times in 20 years of sailing offshore and hundreds of times wandering in shallow spots.

As for through bolting, be careful. I have few through bolts on my boat. I stitch fittings on with uni tow. I also dead end bolts in epoxy. So you may find the screws into the deck have been inserted into an epoxy plug, which is a fine technique. Maybe your boat has these blind epoxy plugs.

cheers

Phil

 

[TomBlake]

Thanks Phil
I've actually purchased those clr257 auto release cleats

I've had two blocks pull off the cabin roof and they were just glued on. A cleat came out and it was screwed through one side of aluminium tubing with no nuts.
Pardon my ignorance. What is stitch fitting with uni tow?

Since we purchased this yacht, we haven't gone out when there's been a really bad chop; so I haven't experienced the rudders coming out of the water.
I've been out in bad chop on a Corsair 24 trimaran(we had for over 10 years) a few times but the single rudder is much longer. No issues there!!
Until a few issues are sorted out, don't really want to tempt fate.

This forum is amazing; with so many people willing to pass their knowledge and expertise.

 

[catsketcher]

Okay, so that is dodgy fitting installation.

I tie composite structures on with strands of unidirectional glass - that is called TOW (rhymes with cow). I pre wet it out on a scrap of plywood and then poke it through holes in the structure, I go round and round, just like tying something with string. When the epoxy sets, it is really strong. My genoa tracks are composite and held on this way. My folding catamaran has all of its hinges held on this way and it is a great way to locate objects whilst having no issues with fasteners or water ingress.

Farriers steer really well. One of the secrets is their really big rudders. All fast monos have nice deep and large area rudders. For some reason some multihull people insist on worrying about wetted surface and reduce rudder area when they should be thinking of low speed control (need large rudders) rudder load after tacking a light multihull (need large rudders) and control on quartering seas when one rudder comes out of the water just as the boat wants to broach (need large rudders).

Of course there are reasons for reducing rudder size - these are usually to do with the problem of beaching a minikeel cat, so the rudders are kept shallower than the keel. As you have kick up rudders and centreboards, you can go nice and large with no worries.

My two folding cats have large rudders and are a dream to tack and steer at low speeds. If I put only one rudder down, and my rudders on my 7 metre cat are bigger and more efficiently shaped than your rudders, the cat goes from being a dream to steer to a typical stallable and harder to tack catamaran. Put both rudders down and she behaves as well as a nice mono at low speeds. It is simple physics of foil loading, often just when we need the rudders to do the most lift we slow down, so we need to size them for these times, not when everything is going nicely in smooth water.

cheers

Phil

 

[TomBlake]

NO! NO! Whoever is telling you that doesn't get it.

Your boat is a multihull with lots of light bits. Having rudders that float is good, they should. But the weight of all the glass you will add will more than make up for the density of hoop pine. Don't use hoop pine. It does not handle water like cedar does and if you drag your rudder onto a rock and go through the glass then the cedar can handle some water ingress far far better than the hoop pine. I love hoop pine but not in foils.

The cedar is a core for the fibreglass. You must put some unidirectional glass on the sides of the rudder. Then the cedar is a core, not a beam. It makes a huge difference to strength. So save the hoop pine for later and get the WRC all set out and buy yourself some 5 to 1 epoxy, about 5 metres of 400 gm uni and 6 metres of 440gm double bias. You also need some silica powder for glue and microballoons for filler.

I can have a look for some plans from other boats if you give me an email

philthompson67@gmail.com

Could you give me some information on when to use the microbaloons and silica and the sequence of 400gm uni and 440gm double bias? I haven't done alot of fibreglassing. What should I cover it with; primer/final coat??
Thanks

 

[Corley]

Can only agree with Catsketcher here, make the rudders bigger it will transform the handling of your boat. I went from a short square section to a longer elliptical plan form on my Tremolino trimaran, it made the boat far better to steer and far less likely for the rudder to stall or pop out in chop. I didn't notice the boat being any slower, seemed about the same with much better handling.

 

[nwguy]

Here's a pic of lengthening both the daggerboard and a rudder for my hydrofoil trimaran. I tapered the bottom ends of both, made divinycell cores for each extension and glued them on with wood flour-thickened epoxy. Then laminated on heavy unidirectional carbon first, followed by other layers of fabric (plain weave carbon biased at 45 degrees to the uni, plus glass over it last). Faired with Total Boat fairing compound. They worked fine. I use Raka epoxy. It's 2:1 so easier to mix than 5:1. Plus they make a nice non-blushing version with a slower cure time.

 

[TomBlake]

Here's a pic of lengthening both the daggerboard and a rudder for my hydrofoil trimaran. I tapered the bottom ends of both, made divinycell cores for each extension and glued them on with wood flour-thickened epoxy. Then laminated on heavy unidirectional carbon first, followed by other layers of fabric (plain weave carbon biased at 45 degrees to the uni, plus glass over it last). Faired with Total Boat fairing compound. They worked fine. I use Raka epoxy. It's 2:1 so easier to mix than 5:1. Plus they make a nice non-blushing version with a slower cure time.

View attachment 158168

What top coat did you use?

 

[nwguy]

Total Boat WetEdge paint. Both boards aren't in the water when not in use.