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Old 04-11-2014, 08:24   #31
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Re: The bow of cats

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Valhalla, we can agree to disagree. In the early days, they were also able to extend the sail area forward through the use of lengthy bowsprits and they did so in spite of the lack of carbon fibre. You are entitled to disagree, but facts are facts.

You suggest that if the LOA is the same, then the plum bow has greater bouyancy forward. I agree. However, as I mentioned, I believe that LOA is a poor standard of comparison for yachts. If the LWL is the same for two yachts, then the boat with front overhang has more bouyancy forward in extremis. This is not just because plum bows tend to have less flare forward (unless they have very fat bows) - it is because as the bow is depressed, the bouyancy of the overhang comes into play. As I said, in heavy weather the bouyancy therefore increases on three, rather than merely two planes. Simple physics, whether you agree or not.

Why do I use LWL rather than LOA in comparing two yachts? I'm sure that even you would agree that LWL is far more important in assessing relative performance, displacement, accomodation etc.than LOA. Indeed, it has only been in recent times that LOA has become so significant in terms of describing (and more to the point, selling) boat models.

As I recall, the first one-design yacht for the New York Yacht Club was the New York 30, early in the last century. It as 40 feet LOA, but the LWL was 30 feet and, as a result, they (and the naval architect, Nathaniel Herreshoff) called it the New York 30. In the era of mass-marketed boats, LOA became the method of describing most models, even though that number was typically less significant than the LWL. Let's face it, a model that was called a '40' certainly sounded better to the uninitiated, than a '30'. If you wish to be a slave to using LOA as the standard of comparison for yachts, you are certainly free to do so. I am not.
If you take two boats of the same LWL, then one that has forward overhang (which adds little to cost) has definite advantages.

I am unsure how you can suggest that the foredeck on two otherwise identical boats would be the same size even though one boat had an added front overhang. If the coachouse remains the same size, then the foredeck is larger on the boat where the bow is extended by overhang. Full stop.

As to reduced spray and resistance to submarining with front overhang, I am sorry that Robert Perry's comments do not make sense to you. You are entitled to your own opinions, just not your own rules of math or physics!

Brad
We will definetly have to disagree because I've yet to find someone who uses the LWL as the primary purchase consideration when deciding how big of a boat they want.

The old 50' boat is a perfect all be it slightly exagerated example to show why LWL is a poor measure of boat size.

I agree, the old clippers used long bow sprits to crowd on more sail...because they couldn't put on taller masts. Long bow sprits are well served structurally by using the overhang as a strong initial part of the extension. So my point still stands, in the days of wooden ships and iron men, there was a compelling reason for overhangs but it was mostly due to a limitation of the material.

No one is challenging the math or physics. But saying 5lbs of silver weighs more than 1 lb of gold doesn't mean the silver is more valuable. Likewise, LWL is a poor measure of vessel size as cost and accomodations are similar with a plumb or moderate overhang (the pointy end doesn't old a lot of accomodation regardless of bow type) but the plumb bow boat will typically be faster and more seaworthy (all else being similar).

Marketing of boats has always been a goofy thing but most people when they get serious don't look at the model number as anything more than a rough idea. When they get serious, they typically start looking at LOA or more realistically the accomodations (both interior and exterior) and LOA correlates to those much more closely to accomodations.
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Old 04-11-2014, 08:33   #32
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Re: The bow of cats

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I've a 38' IP, whose length overall is 41', add dinghy hanging off the stern it's over 45'
I've never paid for more than a 38' boat, do they often actually measure a boat?
I understand that when tied alongside a dock as you take up more dock space, but if your in a slip you taking the entire slip regardless of your length, so is this just done when your on the dock?
This is a different discussion from hull shapes but...

Per the letter of law, you are supposed to provide the LOA including bow sprits, davits or anything else that extends beyond the hull according to most marina contracts.

As long as you fit reasonably into the slip and it's not obviously much longer, it's pretty rare for a marina to challenge the length you tell them (USA experience). Example:
- If you go in with a model X32 and tell them it's 32' but the bow pulpit adds 1' and the dingy on davits adds 3' off the back, odds are they won't say anything.
- If you go in with a columbia 50 and try to claim it's 33' waterline length, you can expect to have a discussion about boat length with the dock master.
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Old 04-11-2014, 08:52   #33
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Re: The bow of cats

A plumb bow gets you maximum waterline length without increasing the length overall. Many marinas charge you for your length overall.
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Old 04-11-2014, 09:31   #34
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Re: The bow of cats

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Originally Posted by a64pilot View Post
I've a 38' IP, whose length overall is 41', add dinghy hanging off the stern it's over 45'
I've never paid for more than a 38' boat, do they often actually measure a boat?
I understand that when tied alongside a dock as you take up more dock space, but if your in a slip you taking the entire slip regardless of your length, so is this just done when your on the dock?
My marina uses a tape measure to determine L.O.A. Everything counts - anchors, dinghys, pulpits etc.. This measurement it used to determine the price of dockage, haulout (travel lift), yard storage etc..

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Old 04-11-2014, 10:12   #35
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Re: The bow of cats

I think we can all agree (and I personally have already acknowledged) that as most marinas charge based on LOA, this is one advantage to a plum bow. I would also like to think that we can all agree that in spite of this, LOA (or LWL) are not the sole criteria in choosing any cruising boat. Nevertheless, for me, in assessing two boats that are otherwise roughly comparable, the LWL is more important than the LOA. Others can and do disagree.

What I cannot understand is how anyone can believe that there are no other differences in performance/traits between a plum bow and one with some front overhang. Does anyone really believe that a plum bow will be as dry as one with some overhang and typically, some additional flare that is permitted by an overhang? Does anyone really believe that the loss of foredeck space is irrelevant on a cruising boat (especially on a monohull or trimaran)? Does anyone really believe that, if one complares two boats with an equivalent design and LWL, the one with a plum bow will have as much reserve bouyancy as one with some overhang and some additional flare? Does anyone really believe that, for boats where the anchor is deployed off the bows, there is no more risk of damaging the topsides on a boat without front overhang (as I have already pointed out, would you really feel secure with an anchor roller that protruded 2 plus feet from the bow)?

Please understand, this is nothing to do with aesthetics. Personally, from an aesthetics standpoint, I actually prefer the look of plum bows on a catamaran. Others may differ. I can even accept the look of plum bows on a monohull - especially one with a performance orientation, as it mimics the look of modern offshore racing boats. I can even understand people who would find the docking costs associated with the increased LOA needed with some front overhang to be prohibitive. What I cannot understand is those who are blind to some of the other factors that come into play when assessing the two different types of bows. Cognitive dissonance perhaps?

Brad
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Old 04-11-2014, 10:36   #36
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Re: The bow of cats

A front overhang bow on a catamaran is like a parking break that activates on every big wave.
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Old 04-11-2014, 10:46   #37
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Re: The bow of cats

I imagine because anything beyond the waterline length is excess weight....
OTOH: I've often wondered if no reserve buoyancy or overhang would make it more likely to dig a bow in in big seas when the cat surfs down a wave though.... pitchpole?
But then you'd need a flared spoon bow to do much good I suppose and that would be real ugly on a cat!
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Old 04-11-2014, 11:21   #38
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Re: The bow of cats

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I imagine because anything beyond the waterline length is excess weight....
OTOH: I've often wondered if no reserve buoyancy or overhang would make it more likely to dig a bow in in big seas when the cat surfs down a wave though.... pitchpole?
But then you'd need a flared spoon bow to do much good I suppose and that would be real ugly on a cat!
Its not the flare that prevents diving, its the volume and you can do it without exaggerating flare. However, many think too much volume contributes to a pitchpoling tendency by stuffing the bows and stopping momentum and preventing them from surfacing quickly.
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Old 04-11-2014, 11:31   #39
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Re: The bow of cats

Yes, Cheechako, all else being equal, the lack of reserve bouyancy through flare and front overhang increases the risk of burying a bow and ptichpoling when running/broad reaching in extreme conditions. For that reason, while you suggest that anything beyond the waterline can be considered 'excess weight', would you have the same opinion if it helped you to prevent burying a bow in heavy seas? Keep in mind, burying a bow/pitchpoling has become an increasing concern in catamarans as the BWL to LWL ratio on many production cats has increased beyond 50%: excessive beam reduces diagonal stability.

Cotemar, front overhang is like a parking brake? Really? So in your opinion, anything which gradually increases bouyancy as the bows are depressed suddenly brings the hull to a screeching halt? So it is better to let the bows sink further into the wave, rather than creating some additional lift? Furthermore, the designers of many new catamaran have made a huge mistake in utilizing upward angled, forward knuckles in order to combat that tendancy and to create some additional reserve bouyancy/lift toward the bows in heavy conditions? Fascinating.

Brad
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Old 04-11-2014, 11:38   #40
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Re: The bow of cats

SVNeko, once you bury a bow in a cat that has significant forward momentum you are likely to picthpole, or at least swing the boat wildly to the lee side where a capsize is a distinct possibility. The idea is to avoid burying a bow at all costs, and all things being equal, a cat with more reserve bouyancy in the bows due to flare and a front overhang is better able to resist burying a bow. I say 'with all things being equal' because a boat with very fine bows and an inverse sheer (lowering freeboard at the bows) is, of course, going to be at greater risk no matter what.

Brad

P.S. SVNeko, I have always loved the Switch 51 - although it is way outside of my 'snack bracket'. However, as I recall it has some front overhang (maybe 12 - 15 inches) plus some rear overhang (as the transoms are elevated out of the water) that provide some reserve bouyancy.
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Old 04-11-2014, 12:05   #41
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Re: The bow of cats

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Cotemar, front overhang is like a parking brake?
Yes, large overhangs on a bow are like parking brakes. They stay under water longer and are slower to reemerge. You get 3knots to 0 knots then repeat, repeat, repeat in large head wind and waves.

Vertical bows cut through wind and waves and act like a bobber and do not stop your boat.
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Old 04-11-2014, 12:42   #42
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Re: The bow of cats

Brad,

A lot of your issues with verticle bows seems more related to the fineness of the entry angle than the amount of overhang. Sure a fine entry is going to result in a smaller bow working room, but that has nothing to do with the plumbness of the bow (or lack thereof).

As for increased pitch poling... Vertical bows, heck reverse bows have been show over and over to reduce pitch poling because it gets weight out of the bows, and allows the immersed section to start working quicker. This is why the highest speed multi-hulls are going to more and more radical bow sections, where frankly hull speed has stopped being a criteria of anything (and yes I know these designs make tradeoffs no cruiser would). But even in more conservative designs like a Gunboat you see plumb bows, pronounced flare, and a lot of boyancy forward.

Some of the Gunboats are even moving to reverse bows (which I think are stupid for cruising) to increase waterline leingth and reduce bow dig. And I don't know anyone who has sailed the Guns who has complained about spray relative to other big cats.
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Old 04-11-2014, 13:12   #43
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Re: The bow of cats

Cotemar, I am unsure what you mean by 'large' overhangs, but I suppose if they were 10 feet long they could tend to get caught up in head seas! In any case, have you actually sailed your cat with the bows (or even one of them) continuously being submerged and then released and then submerged? Good grief, how did you survive? I have never submerged the bow of any boat I have been sailing and, in order to avoid pitchpoling/capsizing, I don't ever intend to.

I am surprised that the boat didn't come to an immediate stop when the front of the bridgdeck came into contact with green water (as it surely must have if the bows were completely submerged). Were you motoring directly into huge wind and breaking waves? If so, why? If you wanted to keep the bows into the seas in those conditions, did you consider depolying a sea-anchor/para-anchor to stop the additional forces caused by your forward momentum?

Alternatively, did you consider running before the storm while streaming warps, a drogue or a series drogue (surely better than sailing or motoring directly into huge breaking seas that are continuously burying the bows). I must say, I bow to your experience, even if I have no desire to share it.

One other question: it strikes me that if the bow of a boat has more reserve bouyancy, then it will not only be harder to submerge, but also faster to bounce back up (think of a bigger 'bobber', to use your expression, with more bouyancy). So are you saying that a smaller, less bouyant bobber would somehow have more upward force to break free of the water? But if the force to resurface is not as a result of encapsulated air -i.e., bouyancy, then what force are we talking about?

Brad
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Old 04-11-2014, 13:55   #44
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Re: The bow of cats

Stumble, Gunboat has also moved towards significant 'knuckles' on the topsides that increase bouyancy of the bows (and in their case sterns) as they are depressed beyond a certain point. I refer to that very design tendancy in post 39 (albeit only reference forward knuckles, as we were discussing only bouyancy in bows). This can indeed compensate for bouyancy lost by the elimination of foreward overhang when the bows are depressed up to the point of the knuckle. Of course, IMO the best of all worlds would be a combination of knuckles and some overhang.

It should also be remembered that Gunboat tend to start their bridgedeck further back from the bows than on most production cruising catamarans that are designed for (or at least in part for) the bareboat charter industry. While this reduces interior space, it does ensure that the Cg of the boat is further back than on many designs - again, reducing the risk of burying a bow (something else I referenced in an earlier post as a means of compensating for a plum bow).

As to spray on the foredeck - apart from Bob Perry's rather colorful comment about plum stems 'making your boat into a submarine', it is clear that a bow with some overhang will have more flare at the start of the waterline (where the bow wave/spray typically commence) than a boat with a plum bow. Otherwise, the plum bow would have to be shaped like a rather large V with a flat leading edge. Amongst other things, flare tends to divert spray to the side, rather than up and over the forward part of the deck.

Again, Gunboat have addressed this to some degree with the use of 'knuckles', which also tend to divert spray to the side. Regardless, I am prepared to (and already did) concede that spray on the foredeck of the hulls of a catamaran is much less significant than on a trimaran or monohull: the forestay/roller reefing gear are installed on the cross member, rather than than the bows, and hence the bows need not be approached in heavy conditions. I suppose that it could still be an issue on cats with a solid foredeck (and thankfully, there are no longer many of those), but otherwise the spray would only be an issue when flying a symmetrical spinnaker off the bows, or attempting to deploy a sea-anchor. I believe that I have already referred to this as well.

I have also already said that I would be prepared to buy a cat with a plum stem (and that I actually prefer the aesthetics of them on a cat). I did, however, caution that I would want the waterline to extend further forward of the Cg of the boat (and hopefully the Ce of the sailplan) than on a boat with some front overhang. I would also want some knuckles, at least on the forward third of the topsides.

Brad
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Old 04-11-2014, 14:02   #45
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Re: The bow of cats

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Yes, Cheechako, all else being equal, the lack of reserve bouyancy through flare and front overhang increases the risk of burying a bow and ptichpoling when running/broad reaching in extreme conditions. For that reason, while you suggest that anything beyond the waterline can be considered 'excess weight', would you have the same opinion if it helped you to prevent burying a bow in heavy seas? Keep in mind, burying a bow/pitchpoling has become an increasing concern in catamarans as the BWL to LWL ratio on many production cats has increased beyond 50%: excessive beam reduces diagonal stability.

Cotemar, front overhang is like a parking brake? Really? So in your opinion, anything which gradually increases bouyancy as the bows are depressed suddenly brings the hull to a screeching halt? So it is better to let the bows sink further into the wave, rather than creating some additional lift? Furthermore, the designers of many new catamaran have made a huge mistake in utilizing upward angled, forward knuckles in order to combat that tendancy and to create some additional reserve bouyancy/lift toward the bows in heavy conditions? Fascinating.

Brad
regarding excess weight... I was simply responding to the question of "why so many are designed plumb"...and suggesting the designer may have had that in mind... not saying it is or isnt my preference.
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