Heaving-to in a Catamaran

[Bash]

[QUOTE=catty;853491]

Originally Posted by belizesailor

The key factor which determines whether a vessel (regardless of number of hulls) heaves-to well is it's lateral resistance characteristics. If the boat has a keel which is relatively narrow fore-and-aft and shoal then the boat probably won't heave-to well. QUOTE]

Yes , I think you have covered 90% of modern cats here.

I disagree. The ability to heave to is a reverse function of a boat's ability to point. The more poorly a boat goes to weather, regardless of the number of hulls, the more narrow the "slot" in which it will heave to.

Any boat that tacks through 100 degrees will heave to more readily than a boat that tacks through 70 degrees. This is why the older full-keelers are so easy to heave to when compared to fin-keeled monos, and why some cruising cats are easier to heave to than racing cats. The less a boat wants to point, the more it wants to heave to.

[44'cruisingcat]

Yet we are constantly told cats can't sail to windward, and now we're told they can't heave to either?

[webejammin]

I'm glad To hear our Gemini 105Mc can hove to too.

[belizesailor]

Originally Posted by webejammin

I'm glad To hear our Gemini 105Mc can hove to too.

Good new/Bad news: it does not heave-to real well.

[belizesailor]

[QUOTE=Bash;853621]

Originally Posted by catty

I disagree. The ability to heave to is a reverse function of a boat's ability to point. The more poorly a boat goes to weather, regardless of the number of hulls, the more narrow the "slot" in which it will heave to.

Any boat that tacks through 100 degrees will heave to more readily than a boat that tacks through 70 degrees. This is why the older full-keelers are so easy to heave to when compared to fin-keeled monos, and why some cruising cats are easier to heave to than racing cats. The less a boat wants to point, the more it wants to heave to.

Given that we agree upon the general design categories of vessels which heave-to "well" versus not (full-keel vs fin-keel respecively), I expect that our primary difference of opinion relates to our respective usage of terminology (specifically "lateral resistance" versus "lift").

So, with that in mind, I am going to expand on the terminology and concepts a bit below (sorry for the long response). Even if we don't ultimately agree it should be an interesting discussion.

First lets define what "heaves-to well" means. I use it to mean: easily assumes a heave-to attitude and maintains approximately a close-reach angle to wind with out excessive mucking about with the sail plan.

When I used the term "lateral resistance characteristics" previously it was in the context of a vessel in a "static" state, e.g., "hove-to". The forces
generated by the keel are different for a vessel in a static state versus a "dynamic" state, e.g., "underway and making headway". When in a hove-to attitude the keel is being pushed laterally through the water. To push a full keel laterally through the water requires an enourmous amount of force. To push a narrow fin keel laterally through the water requires proportionally much less force. Thus a full keel boat heaves-to better than a fin keel boat. In both cases the keels are generating lateral resistance, but, since there is effectively no fore-to-aft flow over the keel, essentially no "lift".

In contrast, when a vessel is in a dynamic state (as defined above), the keel is moving forward through through the water. In this mode it provides not only lateral resistance, but it also generates "lift" which helps drive the vessel to windward. In terms of forces generated by the keel (ignoring for the purpose of this dicussion forces generated by other components of the boat), it is this lift force which primary contributes to the windard and tacking abilities of the vessel -- not lateral resistance per se.

Take for example a Hobie 33. It has a very narrow fin keel which is optimized to produce lift. As a result, the Hobie 33 will sail amazingly close to the wind (polar diagram plots end at just less than 30 degrees). In a static state the H33 keel provides relatively little lateral resistance, but as boat speed, and thus water flow over the keel, increases the lift force increases dramatically as does windward performance. As a result of these characteristics, the H33 also does not heave-to very well (she tends to ocilate through a wide range of wind angles and defintely requires a lot of mucking about with the sail plan to keep her reasonably stable...I own a Hobie 33 so I know this from experience).

In contrast, take a full keeled boat (or at least relatively full keeled) and the behavior changes significantly. Most full keels are relatively flat sided
and are not optimized to produce lift. As a result, windward sailing angles and tacking angles are increased. They do however produce huge amounts of lateral resistance in either a static (hove-to) or dynamic mode of operation. This gives them great tracking stability and excellent heave-to behaivior, but not stellar windward or tacking performance.

Therefore, in terms of keel type and the resulting forces in a static state: it is lateral resistance which primarily determines heave-to behavior. Windward performance and tacking angle are a function of the lift characteristics of the keel operating in a dynamic state.

To round us back up to the subject of this thread "catamarans heaving-to" lets compare two cats in a similar size class that I know: A Moorings 3800
(Robertson & Caine) and a Wildcat 3500 (Charter Cats). Both of these boats have similar effective tacking angles (100+ degrees -- similar to many other production cats), but different heave-to characteristics. The Wildcat has an unusally full keel for a cat -- thus it tracks well and heaves-to quite well. The R&C designs have much less full keels so they don't heave-to quite as well (but they do). Aboard either of these boats, as boat speed increases so does lift from the keel. This allows you to bring the boat up, from it's 100+ tacking angle, to a more respectable windward sailing angle of about 45 degrees as you gain boat speed (the Wildcat in fact will pinch up to just under 30 degrees, but with significant loss of boat speed). If tacking angle were the primary determinant of heave-to behavior then these two vessels would have essentially the same heave-to behavior.

One other example: Cats by Gemini have tacking angles of about 100 degrees also and do not heave-to very well. Thus the statement that "Any boat that tacks through 100 degrees will heave to more readily than a boat that tacks through 70 degrees..." is clearly not true.

Bottom-line (IMHO): In a static state, lateral resistance is the primary characteristic which determines heave-to behavior. Windward performance and tacking angle are more significantly determined by lift in a dynamic state and are much more difficult to clearly map to heave-to behavior.

Caveat: I am a professional sailor not a naval architect -- maybe someone with these credentials could chime in on this discussion?

[Bash]

[QUOTE=belizesailor;854044]

Originally Posted by Bash

Bottom-line (IMHO): In a static state, lateral resistance is the primary characteristic which determines heave-to behavior. Windward performance and tacking angle are more significantly determined by lift in a dynamic state and are much more difficult to clearly map to heave-to behavior.

You've certainly captured the old line of thinking here, the same line of thinking that used to lead to the claim that fin-keeled monohulls couldn't heave to effectively.

Thinking along a more modern vein, what needs to happen in order to heave to successfully on more contemporary designs (boats that accelerate well) is to depower the main in order to keep the boat from tacking through the wind. This isn't hard to do; easing the traveler is often all it takes. Now the main stalls earlier when the boat rounds up, causing the boat to settle back into a space where it will again begin to forereach.

While I will grant you that an older full-keeled monohull design will be less active once hove to, I reject the argument that lighter, more dynamic boats can't heave to. Too many of us, both cat owners and fin-keeled mono owners, have discovered that by adjusting the technique a tad to fit the boat, it can be done successfully, even in a blow.

[boatman61]

[QUOTE=Bash;854062]

Originally Posted by belizesailor

You've certainly captured the old line of thinking here, the same line of thinking that used to lead to the claim that fin-keeled monohulls couldn't heave to effectively.

Thinking along a more modern vein, what needs to happen in order to heave to successfully on more contemporary designs (boats that accelerate well) is to depower the main in order to keep the boat from tacking through the wind. This isn't hard to do; easing the traveler is often all it takes. Now the main stalls earlier when the boat rounds up, causing the boat to settle back into a space where it will again begin to forereach.

While I will grant you that an older full-keeled monohull design will be less active once hove to, I reject the argument that lighter, more dynamic boats can't heave to. Too many of us, both cat owners and fin-keeled mono owners, have discovered that by adjusting the technique a tad to fit the boat, it can be done successfully, even in a blow.

+A1..... its what the boat likes that matters.. not what the text books say..

[webejammin]

With all the discussion on heaving to in a monohull I think this thread has drifted too far good by

[Therapy]

Originally Posted by belizesailor;853607

I have sailed modern production cats by Lagoon, Fontain Pajot, Privilege, [B

Gemini[/B], Robertson & Caine, Charter Cats (Wildcat) and Manta. Certainly a representative slice of the market. They will all heave-to...just some better than others.

I have done it in mild conditions only.

How do you suggest setting the centerboards on the Gem in "worse" conditions?

[belizesailor]

[QUOTE=Bash;854062]

Originally Posted by belizesailor

You've certainly captured the old line of thinking here, the same line of thinking that used to lead to the claim that fin-keeled monohulls couldn't heave to effectively.

Thinking along a more modern vein, what needs to happen in order to heave to successfully on more contemporary designs (boats that accelerate well) is to depower the main in order to keep the boat from tacking through the wind. This isn't hard to do; easing the traveler is often all it takes. Now the main stalls earlier when the boat rounds up, causing the boat to settle back into a space where it will again begin to forereach.

While I will grant you that an older full-keeled monohull design will be less active once hove to, I reject the argument that lighter, more dynamic boats can't heave to. Too many of us, both cat owners and fin-keeled mono owners, have discovered that by adjusting the technique a tad to fit the boat, it can be done successfully, even in a blow.

I agree with you 100% regarding fin-keeled monos (See my comments regarding the H33 in previous post). I don't believe I did imply, nor intend to, that they "can't heave-to". Like cats, fin-keeled monos are not typically as sea-kindly as more traditional keel shapes, but they can be finessed into heaving-to acceptably well.

[belizesailor]

Originally Posted by Therapy

I have done it in mild conditions only.

How do you suggest setting the centerboards on the Gem in "worse" conditions?

I have only hove-to aboard a Gemini in relatively benign moderate conditions as part of sail training for the owner. They will heave-to, but being quite light and a centerboard configuration, not all that well (they do however sail much better than I expected). I can only speculate about heavier conditions. I would go for maximum lateral resistance by making sure the boards are completely down and locked. I expect that keeping their head up in heavier wave conditions could be a challenge due to these same factors.

Although a word of caution: I do know folks who have snapped off centerboards aboard monohulls doing this in heavy conditions. And, of one case where the centerboard trunk failed under the stress and the boat sunk (also a small mono)...fortunately they got her into very shallow water before she went down.

[Therapy]

Originally Posted by belizesailor

I have only hove-to aboard a Gemini in relatively benign moderate conditions as part of sail training for the owner. They will heave-to, but being quite light and a centerboard configuration, not all that well (they do however sail much better than I expected). I can only speculate about heavier conditions. I would go for maximum lateral resistance by making sure the boards are completely down and locked. I expect that keeping their head up in heavier wave conditions could be a challenge due to these same factors.

Although a word of caution: I do know folks who have snapped off centerboards aboard monohulls doing this in heavy conditions. And, of one case where the centerboard trunk failed under the stress and the boat sunk (also a small mono)...fortunately they got her into very shallow water before she went down.

Well hummm.
Maybe one day I will find out.

[belizesailor]

Originally Posted by Therapy

Well hummm.
Maybe one day I will find out.

Be sure and post if you do. Maybe other Gemini owners out there with heavier weather experience on this boat.