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Old 13-05-2016, 16:20   #136
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Re: Pilothouse Variations -- Boreal

I do not mean to challenge the extremely talented Mr. Dashew, but I think this picture is somewhat relevant to the discussion.

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Old 13-05-2016, 16:36   #137
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Re: Pilothouse Variations -- Boreal

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That makes no sense. Consider hull length and the advantages are all on the plumb bow (that is why they are used in modern boat design).

Yes the LOA is bigger but the easiest and more used cruising downwind sail is a geenaker and a gennaker needs a pole. The modern tendency is to have a pole that incorporate an anchor stand. Here another aluminium passagemaker with that type of pole/stand, the Allures 52:
Its just a fashion statement on a heavy cruiser with a prod. Might as well draw the bow out a touch and have less pole/prod. The forestay can stay where it is and you end up with a more open spacious foredeck, and a much stronger anchor roller system. Probably lighter as well.
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Old 13-05-2016, 17:09   #138
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Re: Pilothouse Variations -- Boreal

I must say that Allures posted above has plenty of allure. THX for sharing!

BTW - WATER BALLAST tanks - I could take them - if you can fill just one of them prior to the passage, you get countless fresh water showers, NO?

Then again a watermaker is not a bad thing either ;-) for a cruising purist.

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Old 13-05-2016, 17:20   #139
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Re: Pilothouse Variations -- Boreal

BTW nice shot of that Dashew ;-) too ... ;-)

I am not sure powerboat and sailboat hulls can be compared 100% BUT the picture stands and has big explanatory value!

I was thinking about this thing today. I was remembering Portuguese fishing boats with their distinctive flared out bows.

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Old 13-05-2016, 17:53   #140
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Re: Pilothouse Variations -- Boreal

Barn, I agree that comparing different hull types is problematic. There are multitudes of factors that we are not even mentioning, let alone understanding fully as amateur (wannabe) naval architects.

That said, it could be argued that the Dashew FPB hulls are more sailboat like than Panope's hull (which is a lot like some of the older, slow fishing boats).

Panope has the same power to weight ratio as the FPB (most would say Panope is overpowered). I have powered dead into an honest 40 knot wind chop (2 meter) and although the larger waves will slow the boat, they do not come aboard. I even had to venture forward to tame a flogging head-sail. It was like riding a bucking bronco (a gentle one because Panope has a LOT of weight in her bow) but no green water aboard.

Here is a shot of Panope motor sailing to a schedule (going like hell - 7 knots) into a 1 meter chop. The hull does not have the 'sculpted' flares seen on some powerboats. Instead. the hullsides (being flat plate) are tipped outboard just enough to eject the water outward.

Not the fastest hull shape but for me, possibly the safest.

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Old 13-05-2016, 18:28   #141
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Re: Pilothouse Variations -- Borealis

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The flare has another advantage, a serious one, of giving a bit more deck space there where you are handling ground tackle, working on furlers, dropping sails, climbing on and off the bow when moored Baltic-style.
Also on a metal boat, an integral bow spirit pushes that space even further fwd to improve forestay angles and to keep chain from fouling bow.

My small bulwark around the bow spirit creates a very strong box structure and a secure location when working there.
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Old 13-05-2016, 22:52   #142
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Re: Pilothouse Variations -- Boreal

Hi all, I've been away for a bit. I see that there was a question or two about Rocket Science.

First, regarding water ballast- It makes all kinds of sense if it's done right, and it really doesn't have to be that complex.

The optimum placement of the ballast tanks is up high, and way out at the edge of the hull. Rocket Science carries 200 gallons on the windward rail, as does at least one other Bieker design. It is not a huge amount of weight for a 55 footer, even one displacing only 24,000 lbs. Heel is reduced by about 5 degrees on average. The other benefit is that it really tends to settle the boat down. It does a ton of good when close reaching and sailing to weather, essentially giving the boat more driving force when it's needed.

And, the best part? When conditions are lighter, that weight can be simply drained back into the ocean in just a couple of minutes by opening a single valve. Really, it's just a lot of 'rail meat' that we don't have to feed or house.

I absolutely love it. The pump is a simple 110v centrifugal unit. I've gotten rid of the more complex aspects of the system as it was originally designed. Now, the fill/transfer/dump valves are turned by hand, the pump is turned on, and that's that. Emptying a ballast tank requires no electricity.

For the fellow interested in the build, the link has been posted here on page 6. There is a pretty detailed description of the boat on our site.


I fully understand the reservations about a plumb bow. As I've mentioned before, on this thread, the foredeck on RS is quite wet. We don't particularly mind, having owned a boat with a clipper bow and a ton of flare. I prefer to keep moving forward fast with a wet deck than hobby-horsing up and down and getting drastically slowed down by all that flare, while still having a wet foredeck anyway.

It's just a personal preference, and Dockhead's points are well taken. We have had to change the way we had typically sailed in bad weather because of our boat's design, which I don't find to be a big deal. We slow right down by pinching up or bear off to handle foredeck work, and that keeps things reasonable up forward. I have not yet been out in truly bad weather on RS, maybe I'll change my opinion after a F10 blow about this. Generally, I think that we'll manage perfectly well with our fine bow. In any case, we have a lot of flare in the hull, so RS is certainly not one of the worst offenders out there on this front.

Of course, the ability to make very fast passages does reduce the risk of encountering such weather.

This is a bit off of the original intent of the thread, apologies for that. If anybody wants to get a little further into the weeds on design detail, send me a pm.

TJ
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Old 14-05-2016, 08:24   #143
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Re: Pilothouse Variations -- Boreal

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Now this is a sweet shot too!

I agree what is fasssssst & good for some may be less than optimum for others.

We are lucky to have so many varied designs around to chose from.

As for the Dashew boat, I think there are at least two things involved: one, that shot is specific, I do not think the boat is doing this every day ;-); two, there will be VAST differences between this one and any sailing boat - where the center of gravity is, where the center of driving force is, how weight is distributed, how much power is under the pedal and how this power self-depowers (or not) depending on how a sailing boat moves her rig thru the air in rough seas. Things can be compared but it would call for a longer analysis that could in the end find just what we find intuitively - boats differ.

Looking at your picture I found myself in the state of travel itch. Meanwhile, there is a major scrub and polish exercise for me thru the day and then maybe some more foruming in the evening. ;-)

Cheers,
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Old 14-05-2016, 11:32   #144
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Re: Pilothouse Variations -- Boreal

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Its just a fashion statement on a heavy cruiser with a prod. Might as well draw the bow out a touch and have less pole/prod. The forestay can stay where it is and you end up with a more open spacious foredeck, and a much stronger anchor roller system. Probably lighter as well.
You should really like very fast and light cruising boats to call a boat with a D/L of 166 a heavy cruiser

Normally with that D/L it would be called a performance boat even if it is not a case: Just a modern relatively fast bluewater boat.

The bow has nothing to do with a aesthetic statement but with efficiency and that's why contemporary designs have those type of bows, except the few ones that indulge in a classic look, merely for aesthetic reasons. Quite the opposite of what you say, starting on the heavy boat and finishing on the aesthetic motivation regarding design
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Old 14-05-2016, 11:45   #145
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Re: Pilothouse Variations -- Boreal

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Hi all, I've been away for a bit. I see that there was a question or two about Rocket Science.

First, regarding water ballast- It makes all kinds of sense if it's done right, and it really doesn't have to be that complex.

The optimum placement of the ballast tanks is up high, and way out at the edge of the hull. Rocket Science carries 200 gallons on the windward rail, as does at least one other Bieker design. It is not a huge amount of weight for a 55 footer, even one displacing only 24,000 lbs. Heel is reduced by about 5 degrees on average. The other benefit is that it really tends to settle the boat down. It does a ton of good when close reaching and sailing to weather, essentially giving the boat more driving force when it's needed.

And, the best part? When conditions are lighter, that weight can be simply drained back into the ocean in just a couple of minutes by opening a single valve. Really, it's just a lot of 'rail meat' that we don't have to feed or house.
....
TJ
Just to back up your statement with some solid data we can have a look at the studies Finot made many years ago for the first version of Cigale (that had water ballast), his ideal cruiser, the one he designed for himself. You can see the difference in what regards power and the need to reef much sooner if the water ballast (1000kg) was not used: From over 20k close upwind with full sail to the need to reef at 16k.


The differences in speed are also very significant.
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Old 14-05-2016, 13:48   #146
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Re: Pilothouse Variations -- Boreal

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Just to back up your statement with some solid data we can have a look at the studies Finot made many years ago for the first version of Cigale (that had water ballast), his ideal cruiser, the one he designed for himself. You can see the difference in what regards power and the need to reef much sooner if the water ballast (1000kg) was not used: From over 20k close upwind with full sail to the need to reef at 16k.


The differences in speed are also very significant.
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This is very interesting data, thanks for posting it. Very different from the Kanter information.

Water ballast is back on the front burner
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Old 14-05-2016, 17:00   #147
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Re: Pilothouse Variations -- Boreal

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You should really like very fast and light cruising boats to call a boat with a D/L of 166 a heavy cruiser

Normally with that D/L it would be called a performance boat even if it is not a case: Just a modern relatively fast bluewater boat.

The bow has nothing to do with a aesthetic statement but with efficiency and that's why contemporary designs have those type of bows, except the few ones that indulge in a classic look, merely for aesthetic reasons. Quite the opposite of what you say, starting on the heavy boat and finishing on the aesthetic motivation regarding design
Raking the bow a few degrees forward would not effect the efficiency of that boat one bit. That would be true if the rake was taken from the waterline length. But if a bit of extra length was added to the deck the boat would be dryer., and the prod would be shorter, stronger and lighter.

It just wouldn't look as "modern" and uninformed people would go on about how it was sacrificing waterline length...

Almost all cruising boats are heavy compared to modern racing boats. Its not just the weight but the longitudinal moment of inertia thats important. Race boats go to extreme's to reduce this by centralising all weight. A cruising boat has anchors, chain, windlass, samson post, fancy interior filled with gear forward. Plus typicaly a much heavier mast. And a bunch of heavy stuff aft like dinghys and all the cockpit locker clutter.

So a cruisng boat generally needs a touch more bouyancy forward to help keep the decks a bit dryer.

The exceptions are more extreme boats like the dashews and rocket science that have gone to great lengths to keep the d/l under 100 and the ends light. On them the plumb bow makes sense, its a good way to reduce pitching motions on a very light boat.

The only measurement that really counts to a cruising boat is the length the marina is going to charge. And most marinas will count that little bowsprit as extra $$

Heres a question for you, are the new reverse bows on the latest VOR boats all about efficiency, or looks? should cruising boats adopt this latest trend? If a plumb bow is better than a raked bow, surely a reverse bow is better again? Where do we stop..
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Old 14-05-2016, 22:27   #148
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Re: Pilothouse Variations -- Boreal

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Heres a question for you, are the new reverse bows on the latest VOR boats all about efficiency, or looks? should cruising boats adopt this latest trend? If a plumb bow is better than a raked bow, surely a reverse bow is better again? Where do we stop..
While racing crews want to get wet there's a limit how wet they want to be and it's good to have a look forward once a while without getting half of the sea pouring on your face. So raked bows keeps the submarines a bit dryer by shaking some of the water of the deck. Rigs are taller and not so much deck length is needed for high aspect bladed sails and when they need it there's that high tech carbon bowsprit costing more than my boat..
For a cruiser... I have a VOR cap and that looks cool too LMAO
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Old 15-05-2016, 04:44   #149
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Re: Pilothouse Variations -- Boreal

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. . . The exceptions are more extreme boats like the dashews and rocket science that have gone to great lengths to keep the d/l under 100 and the ends light. On them the plumb bow makes a lot of sense...

Indeed. There are not only many tradeoffs, but also very different effect of the bow form, on different boats, so there is no "one size fits all" answer, like "plumb bows are modern; others are just stupid".

A tendency to hobby horse is something you get with a boat with light ends and low polar moment of inertia, but you also get dryer decks because the bow rises up more responsively. Such boats have less need of bow rake and flare.

But the optimum tradeoff of hobbyhorsing versus dryer decks will also be different, for boats used in different latitudes and conditions. In very cold and very rough weather, you will tolerate more hobbyhorsing to keep the green water off the boat.


So the bow has to be designed as an integral part of the whole design of the boat, and it is really stupid to talk about this or that bow form being the only right form, for all boats, and all conditions. The progression of buoyancy at the bow is part of the "tuning" of the dynamic qualities of the hull.


If the designer succeeds in making a boat with very low polar moment of inertia, and particularly if the boat is long enough, then you can get a very desirable situation where you need little or no flare or rake, and can make the bow rather fine, which allows the boat to "cut" through the waves without, however, going under them. This will make the boat faster since flare particularly takes away fineness of the bow entry and makes the boat slower, and will give a smoother ride.


But in my opinion few boat designs in production have actually earned the right to plumb bows; these boats are definitely wetter. Particularly boats under 45' or so -- I think the plumb bow is often just a fashion statement, not backed up by proper engineering. I spent a couple of seasons sailing a Salona 45 in the Adriatic, a great sailing boat which I loved, but with an almost plumb and very fine bow, it was a horrible submarine even in the mild conditions of the Med. A very moderate chop would result in sheets of green water sweeping the decks. I can't even imagine sailing a boat like that in the Atlantic.

As I mentioned, my own boat with mild rake and zero flare (weird since the stern is strongly flared) likewise has inadequate buoyancy in the bow, or inadequate progressivity of the buoyancy. And almost no tendency to hobby horse, so could very well afford a bit of flare. I think the bow was designed for a certain look, and without enough attention to dynamics of the hull. Also probably I have exacerbated the situation by putting 330kg of chain in the forward chain locker, but a serious cruising boat of this size should be able to carry 100 meters of chain, in my opinion, without adverse effect on handling.
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Old 15-05-2016, 07:19   #150
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Re: Pilothouse Variations -- Boreal

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Just to back up your statement with some solid data we can have a look at the studies Finot made many years ago for the first version of Cigale (that had water ballast), his ideal cruiser, the one he designed for himself. You can see the difference in what regards power and the need to reef much sooner if the water ballast (1000kg) was not used: From over 20k close upwind with full sail to the need to reef at 16k.


The differences in speed are also very significant.
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As well as going faster by carrying more sail you can choose to sail with the same sail area at less heel for more comfort and less leeway with water ballast.

Just out of curiosity, I looked at my boat's GZ curve and I work out that to reduce heel from 20deg to 15deg I would need about 1.9 tons of water ballast. Certainly achievable in a new build. A fair price to pay in loss of hull volume though.
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