Weather helm on starboard, port OK

take the main halyard to the end of the aft beam and then to the other end to see if mast is leaning to port or starboard

 

Thanks for that! I hadn't considered the effect of speed on small changes, but you're right, on the Hobie, the tiniest thing makes a big difference when moving fast. Good Point.

And yeah - we averaged 14 knots for quite a while Saturday, bursting to 17 then and again.

Phil - Thanks! So there is some Ackermann compensation. There is a plate on the inner side of each tiller to which the tiller bar attaches You can see it in the first pic. I don't know if the proportions are correct necessarily. I've read that 10 degrees is reasonable at full rudder swing, but will try to measure. I always thought that really came into play during tight turns or tacking versus simply holding a course, but it might be I just don't have a enough info yet.

Team VMG - I'll try the halyard trick...

BTW - Do you guys recommend daggerboards fully up when heading down wind/broad reaching on a boat like this? It seems like it would be squirrely at high speed.

 

The halyard test reveals a 1" difference (shorter on port side). Given this is a homebuilt boat, I'm not sure if that is significant. There's a whole lotta variables driving that measurement! The boat seems square, symmetrical and tight, but you never know! EDITED: As interest, using the spinnaker halyard to each end of the bow crossbeam confirms the halyard test.

I will adjust the shrouds accordingly and try it out this weekend. I wanted to rake forward a bit anyway, so will loosen the port side and give it to the forestay until the halyard measurement is even.

Thank you all for your patient and carefully considered approaches.

 

Not enough to worry about.

Can you measure the diagonals across the tramp to see how square the boat is?

 

I just measured. I don't have the hull centerlines marked, but from inner forward beam bolt to inner aft beam bolt, the diagonals are equal length.

Feelin' pretty good on that!

My intention is to ease the port shroud 1", take it up on the forestay (1" is all that is remains on the turnbuckle!) If more tensioning is needed, I can take it up on the dolphin striker nut. The dolphin striker rod "floats" though the main crossbeam to the base of the mast rotation plate.

See any issues with this approach? Or would I be better served by easing the port shroud 1" and then just using the dolphin striker nuts to increase tension?

Also you might want to know that these are Dynex Dux heat stretched Dyneema shrouds and forestay.

 

I don't think 1" difference will need 1" adjustment, so small movements first.
I do find on my cat that would be enough to notice sailing upwind when fully powered up, but still very minor. would not notice downwind, so do dont think that will be the answer.
My boat has ackerman set up like yours (offset from straight tiller), but about 300mm long? But again, only an issue when turning i thought, not straight lines.

The worst answer no one has mentioned, is that you cb cases are not parallel?

 

Gday Pax

There is something nice about being able to give advice to someone who isn't asking a silly question. I think with all the flex your typical movable Tennant cat the structure will alter somewhat in geometry.

As to Ackerman - you are right. It should only be a concern when turning. There is a concpet called toe in which beach cat sailors talk about but they fly a hull a lot. I would still be interested in seeing how the rudders align when one is let free. In fact I would be interested, now that I can see that your rudders have balance due to being raked forward if what you were getting was rudder loading and not really weather helm.

On my 6 metre cat I made the rudders without balance and they gave quite a tug on the arm. I then cut in some balance and they went to finger tip helm required plus the boat seemed to have less effective weather helm as the CP and pivot point got closer.

You may find that putting both rudders down fully will reduce helm as they will gain balance ahead of the CP

cheers

Phil

 

more thoughts - not having enough cb down can load up the helm when reaching.
so ensure you have enough board down to balance. or did you mention that?

 

Thanks Phil. I have several questions.

Can you tell me what the term "rudder loading" refers to, and how it differs from weather helm?

I had both rudders down the entire time. Given their location and the precarious gymnastics required to raise and lower them, I don't change their height while underway. Especially since the water was 10 degrees C Saturday!

We did vary the daggers up and down alternately, and found that raising the windward dagger reduced weather helm by maybe 10%. We figured that was simply the reduced drag of having the dagger out. We were moving at 14 to 15 knots at that time.

Finally - you mentioned "letting one of the rudders free." What are you suggesting there? Disconnecting the tiller crossbar and sailing on one rudder to see how the other reacts?

 

Clipper - you might be on to something here. According to the plans the boards should go down about 4 feet (1.2 meters) and still have the top properly supported inside the case.

The cases get tight about 3 feet down, and we stopped pushing there thinking that was the limit of their travel. But, some coaxing just now shows it can go down 4 feet without issue. Looking back at the video, I can see the push pole (shovel handle) was up higher by maybe another foot!

CLR will move back by ensuring they are down, I'll report back on the change in helm with this approach and the other items we have discussed.

THANKS to All!

 

Are you able to swap the port and starbord rudder blades and cb's over?

 

Gday Pax

When I balanced my rudders on my small cat I didn't change any hydrostatics. The loading on the foil of the rudder must have remained the same to counter the constant weather helm the boat/rig was producing. The more balanced rudder needed less pull on the tiller to stay at the same angle of attack and so the torque on the tiller went down - the "felt" weather helm went down but the rudders were still coping with the same weather helm from the boat's torque.

I am not sure if the boat turned into the wind slower, she is mothballed at the moment so I can't go play and see but I think she became a little easier too. Certainly she was very nice to sail with the balance.

Big rudders like yours are good and a bit of weather helm can be great in a racer. It means your rudders are developing lift when going to windward. Racing monos have been doing loading rudders for decades and I think most cats have rudders way to small to do this but your nice deep foils can cope with loading.

If you want to know if your rudders are working well together you can unbolt one end of the tiller arm when sailing and watch the other rudder follow the boat. It should follow the end of the arm closely - I would do this in flat water and on a sedate broad reach with a friend gently holding the tiller arm above the deck. If there are any problems in geometry the tillers will not be in synch.

If I can add one more possible thing to the mix - I would check the rudders for slop and rake as well as swapping them like VMG says. I would also be interested in you sailing with only one and seeing how the balance was affected - when the water warms up. Here on Lake macquarie we never get water below 14 degrees so you have my sympathy.

cheers

Phil

 

Well Gentlemen, after a few tweaks on Friday evening, we had a couple of very nice trips over the weekend. Based on your responses, we made two changes. We eased the port shroud and gave it to the forestay. This seems to have helped the disparity between weather helm on the two tacks. it still favors the port tack a bit, but in retrospect, I think my previous boats generally favored one tack over the other, by a bit.

Taken by itself, it also reduced weather helm a bit on all points.

More importantly, after reviewing the architect's plans and measuring the daggerboard "full down" positions, we realized we had another foot (30cm) that we could extend the daggers. Obviously, This went a long way toward alleviating the weather helm issue, and for the most part, I think it is acceptable now.

I'd like to thank you all for taking the time to contribute to this thread. I learned a lot, and hopefully others can pull some good information from this.

 

Great - all fixed and I didn't even have to epoxy anything!

cheers

Phil

 

You're a Gentleman, Phil!

You could have just as easily said "Bloody Yank didn't put 'is bleedin' boards down!"

cheers

As interest Guys, spring has sprung up here in the Northern Hemisphere, as evidenced by this funnel cloud about 5 miles North of my place last night.