Optimal Heel Angle

[bob perry]

It's Friday so I might as well get the pot stirred for the weekend.

Rover:
I have a busy day today so at the risk of sounding "terse" I'll keep my answers short and you can assume each comment is preceeded by "with all due respect". And yes, there are always exceptions.

In short, with all due respect, I think you are wrong on just about everything you said. Forget about today's fat assed boats. Let's go back to the 50's and 60's with skinny, deep boats and many with full keels and odd CCA and IOR hull shapes. Everything is done by the designer to increase stability. Increased stability was ALWAYS a target of design. That's why both the IOR and CCA had elements in thejm to penalize stability. No one wants to sail heeled over. Of course you balance the innefficiency of heeling against the horse power provided by the rig at that heel angle and many times the hp wins the battle. Horse power is good and more hp at a lower heel angle is REALLY good. But given the choice you sail the boat as upright as possible while using the max hp available.

I do not think a slack bilged boat needs some heel angle to sail at optimal speed. I would use some heel in very light air so the sails fall into an efficfient shape. But that's the only reason.

( for an in depth look at the effect of overhangs on boat speed read the chapter in my book where I use VPP's to evaluate he effect of heel angle on sailing length and bat speed). There's another good argument for another day.

Excesive weather helm is a design flaw regardless of the type of boat, full keel or fin keel. Yes, you can overcome the drag by pushing the boat hard but you would be far better of with helm angles bellow 4 degrees. Drag is not good. If you have to "trim out" the helm at the cost of speed this indicates poor design. There are many. many full kele boats with little weather helm and many with none. Have you ever sailed a 12 meter or a 6 meter? They have full keels and slack garboards but they also have dead neutral helms in moderate air. For the boats of the era we are discussing weather helm comes from having the keel too far forward ( center of pressure) or the rig too far aft ( center of pressure). Baggy old sails and a poorly tuned mast can also add helm.

My philosophy is to always try for a near neutral helm. It's always possible to dig up some weather helm if you want it and sometimes you do want it, but it's not always poosible to get rid of excessive weather helm wihout compromising sail trim. I hate poorly balanced boats.

I'll start piling up the sandbags now.

[S&S]

15 degrees? Reef at 20? LOL! For us 25-30 degrees of heel IS sailing flat LOL! Boat tracks fine at that angle but ours is pretty much the definition of slack bilge, skinny and deep.

Like Bob says above, tippy boat with a big rig.

[NotQuiteLost]

Somewhere in all of this is a reference to multihulls staying nearly 100% upright, and their improved sailing performance over monohulls. But I can't quite find it.

[daddle]

Originally Posted by NotQuiteLost

Somewhere in all of this is a reference to multihulls staying nearly 100% upright

Nice try. Good multi sailors know that the same trim issues that cause excessive heeling in monohulls causes excessive leeway and drag in multis. So this discussion actually applies the same to both.

[bob perry]

I agree with S&S. Most "normal" boats can sail their best when powered up to heel between 25 and 30 degrees. It's not about the hull or foils being more efficient a that angle because they are not. It's about harnesssing the horsepower.

I was racing with a client on his Ultimate 20, a light modern boat. He was insistant that the boat be sailed upright with a big "bubble" in the main to depower it. We were getting our ass kicked. We were flat and we were slow. After rounding the leeward mark I asked, "May I drive?" So I took the tiller and the mainsheet and told the client and his wife to "hang on". I cranked in the mainsheet and let the boat heel a good 25 degrees and we took off. If we had three more crew with an extra 540 lbs. on the rail we would have been even faster.

[slowshoes]

[QUOTE=capbillh;570331]with the original fixed 3 blade prop, it took large helm angle to keep it down when over at 15-20 degrees. But when I replaced it with a Kiwiprop, the weather helm was halved thus I went faster with less drag from the rudder. QUOTE]

capbillh,

Interesting - any idea why a fixed 3 blader would induce so much weatherhelm? I've often wondered whether the fixed 3 blade prop on my boat contributes to weatherhelm. I've never read anthing to suggest that this could be happening - anyone have any thoughts?

[bob perry]

Slow:
The only thing I can think of is that the vortex of the big fixed three blade makes the rudder foil less efficient so you need more rudder angle to do the same job.
Yeah, that's it. Makes sense to me.

[slowshoes]

Originally Posted by bob perry

Slow:
The only thing I can think of is that the vortex of the big fixed three blade makes the rudder foil less efficient so you need more rudder angle to do the same job.
Yeah, that's it. Makes sense to me.

Bob, Thanks for the reply. Do you think it make sense for most boats to replace their fixed 3 blade prop with a 3 blade folding prop then? (or at least on boats that are dealing with a fair share of weatherhelm?)

[bob perry]

Slow:
I think a 2 blade folder would be fine. Dragging a 3blade fixed prop is liike dragging a bucket. Not good. But I'm not sure it will cure all weather helm problems. I haved never really considered or read about the effect of the prop on weather helm. I'm learning too.

[Bash]

Originally Posted by bob perry

I haved never really considered or read about the effect of the prop on weather helm. I'm learning too.

I've had two boats come with fixed props that I sailed for a few months before switching to folding props. While performance improved dramatically in both cases, I don't recall the change having made any difference in terms of weather helm.

[bob perry]

Bash:
I think we are limirted here to boats with pops in apertures where in some cases the aperture can be 20% or more of the total rudder span. So add turbulence off the aft end of the hull cutout, the crudely radiused front end of the rudder portion of the cut out and the area of the three blades and you have seriously reduced the effectiveness of the rudder.

I do not think this would apply to most modern designs with props out in the open.

[slowshoes]

Originally Posted by bob perry

Bash:
I think we are limirted here to boats with pops in apertures where in some cases the aperture can be 20% or more of the total rudder span. So add turbulence off the aft end of the hull cutout, the crudely radiused front end of the rudder portion of the cut out and the area of the three blades and you have seriously reduced the effectiveness of the rudder.

.

That would definitety be my boat - older designed full keel with cut away forefoot and prop in an aperature.

I've never really considered replacing my fixed prop because it's simple, and simplicity rarely lets you down. I'll try to find more research on prop choice and weatherhelm - lord know's I'll have time during the winter months......sigh.

[bob perry]

I think this little drawing will illustrate what Slow is talking about.

[seabee]

Seabee---a few years ago my wife and I got caught in a sunny afternoon storm on lake michigan, we went from 12knot and 2' sea to 35 knot and 18 to 20' sea in about 3min. flat. and by the time I got rigged down to handle it we were heeling over at about 35 to 45 deg. and when we sold the boat it still had little brown marks on the seats.So heel is a matter of how much my wife will handle without saying (OH MY GOD OH MY GOD ) so I run her at about 12 to 15 degree heel and stay married ------SEABEE

[NotQuiteLost]

Originally Posted by daddle

Nice try. Good multi sailors know that the same trim issues that cause excessive heeling in monohulls causes excessive leeway and drag in multis. So this discussion actually applies the same to both.

Well, if we're going to be passive-aggressive about it, the title of the thread is "Optimal Heel Angle," and the best definition I've found of the term 'heel' as it applies to sailing is:

The amount of leaning angle of a vessel under sail

So my point stands just fine, thank you very much. But if we're actually interested in exchanging information, then we can do that instead of sniping weak barbs back and forth. Your call, I s'pose.

The greater point of the discussion, to this point, has been determining optimal performance of a given hull under various angles of heel. Pointing out that the primary purpose of a multi-hull design is to counteract the 'heel' effect in order to greatly improve sailing performance (compared to monohulls) is a valid contribution to the thread.