Re: [bolger] Re: Box Keel discussion
Van de Stadt, a very well known dutch designer, built 1949 the Zeevalk, a 36 ft racing light displacement with very hard chine (but not a flat bottom-boatt)for a plywood-fabricant.
This boat, the first hardchine boat within the light diplacements yachts of that time was very successfull in races and had a keel 1/6 wide of the boat. An additional rudder behind this keel for trim purposes. Not very deep this keel, but much shorter and guessed 3timess deeper as a bolger-box-keel on a sailing boat would be.
Will say: Keels with a remarkable volume and a slim hard-chine-boat worked very well together.
Dieter
"Philip Smith" <pbs@...> schrieb:
This boat, the first hardchine boat within the light diplacements yachts of that time was very successfull in races and had a keel 1/6 wide of the boat. An additional rudder behind this keel for trim purposes. Not very deep this keel, but much shorter and guessed 3timess deeper as a bolger-box-keel on a sailing boat would be.
Will say: Keels with a remarkable volume and a slim hard-chine-boat worked very well together.
Dieter
"Philip Smith" <pbs@...> schrieb:
> < I've spoken with Phil and Susanne about bulbous bows.
> They think that bulbous bows are expensive, work only
> in certain limited conditions of sea and speed and
> displacement and are generally a waste of time and
> money.
>
> The general point of the conversations was that if you
> are worried about speed and you have the money you'd
> be better off increasing the waterline length of your
> boat by five or more feet than adding a bulbous bow.
>
> Given the general tennor of our conversations it is
> probably safe to say that PB&F has not designed a boat
> with a bulbous bow nor are they likely to.
>
> Phil Smith
>
>
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I've spoken with Phil and Susanne about bulbous bows.
They think that bulbous bows are expensive, work only
in certain limited conditions of sea and speed and
displacement and are generally a waste of time and
money.
The general point of the conversations was that if you
are worried about speed and you have the money you'd
be better off increasing the waterline length of your
boat by five or more feet than adding a bulbous bow.
Given the general tennor of our conversations it is
probably safe to say that PB&F has not designed a boat
with a bulbous bow nor are they likely to.
Phil Smith
They think that bulbous bows are expensive, work only
in certain limited conditions of sea and speed and
displacement and are generally a waste of time and
money.
The general point of the conversations was that if you
are worried about speed and you have the money you'd
be better off increasing the waterline length of your
boat by five or more feet than adding a bulbous bow.
Given the general tennor of our conversations it is
probably safe to say that PB&F has not designed a boat
with a bulbous bow nor are they likely to.
Phil Smith
--- Inbolger@yahoogroups.com, James Pope <jpope@a...> wrote:
be like the front of modern submarines which are noted for their speed
and efficency (quiet).
hull, at least when compared to conventional hulls.<<<
I believe that on Bolger planing designs, like Hawkeye, and
Microtrawler, the box keel serves as a "planing hull" with
characteristics of a better than 6:1 sharpie with hard chines. Off
plane, it serves as a keel, providing directional stability.
> Bruce Hallman wrote:No expert, but the bulbous bows always looked like they were trying to
>
> > Has Bolger ever designed a boat with a bulbous bow?
> >
be like the front of modern submarines which are noted for their speed
and efficency (quiet).
>>I think the box keel cheats the standard calculation of displacementhull speed a little bit, by spreading out the wave making effect of the
hull, at least when compared to conventional hulls.<<<
I believe that on Bolger planing designs, like Hawkeye, and
Microtrawler, the box keel serves as a "planing hull" with
characteristics of a better than 6:1 sharpie with hard chines. Off
plane, it serves as a keel, providing directional stability.
Bruce Hallman wrote:
rockered bottom above it with its flat extensions out to the chines
works at the wind/wave interface. This may be a key to why his box keel
boats drive so easily at speeds well above the traditional hull speed
limits.
Another gadget which could increase steady long distance efficiency
might be little turbine blades attached to the hull just forward of the
propeller which would set the water running past the hull into a
rotation countering the wheel's rotation as it sweeps aft into the prop.
An article I read a while ago claimed a 10 or so percent improvement on
some vessels they studied.
Jim
>http://members.shaw.ca/diesel-duck/library/articles/bulbous_bows.htmPCB's box keel accepts most of the boat's displacement while the
>
> Has Bolger ever designed a boat with a bulbous bow?
>
>
rockered bottom above it with its flat extensions out to the chines
works at the wind/wave interface. This may be a key to why his box keel
boats drive so easily at speeds well above the traditional hull speed
limits.
Another gadget which could increase steady long distance efficiency
might be little turbine blades attached to the hull just forward of the
propeller which would set the water running past the hull into a
rotation countering the wheel's rotation as it sweeps aft into the prop.
An article I read a while ago claimed a 10 or so percent improvement on
some vessels they studied.
Jim
> As your subsequent post implies, Bruce, a bulbuous bow is a way ofThe bulb, pushes the bow down and the stern up, canceling some
> doing what PCB wants to do with the box keel (on displacement hulls) -
> - reduce wave-making resistance by spreading the displacement towards
> the ends of the hull, thus increasing the prismatic coefficient.
of the wake. It seems that on a constant velocity cruiser, such as
Tahiti, some sort of bulb like appendage might make sense.
As your subsequent post implies, Bruce, a bulbuous bow is a way of
doing what PCB wants to do with the box keel (on displacement hulls) -
- reduce wave-making resistance by spreading the displacement towards
the ends of the hull, thus increasing the prismatic coefficient. I
don't know any Bolger designs that use it. There have been several
sailing catamaran designs with bulbuous bows.
A similar idea is the "dreadnought bow". Rather than providing an
unwieldy link, I'll let those who are interested find the pictures
with their search engine. On the original Dreadnought the bow was
also meant to act as a ram, but that was not its only function. Early
last century there was a minor craze for this kind of bow on quite
small pleasure cruisers. There was a 40-footer I used to see
regularly -- had a trip on it once -- on the Gippsland lakes.
Howard
doing what PCB wants to do with the box keel (on displacement hulls) -
- reduce wave-making resistance by spreading the displacement towards
the ends of the hull, thus increasing the prismatic coefficient. I
don't know any Bolger designs that use it. There have been several
sailing catamaran designs with bulbuous bows.
A similar idea is the "dreadnought bow". Rather than providing an
unwieldy link, I'll let those who are interested find the pictures
with their search engine. On the original Dreadnought the bow was
also meant to act as a ram, but that was not its only function. Early
last century there was a minor craze for this kind of bow on quite
small pleasure cruisers. There was a 40-footer I used to see
regularly -- had a trip on it once -- on the Gippsland lakes.
Howard
--- Inbolger@yahoogroups.com, Bruce Hallman <bruce@h...> wrote:
> I think the box keel cheats the standard calculation of
displacement
> hull speed a little bit, by spreading out the wave making effect of
the
> hull, at least when compared to conventional hulls.
http://members.shaw.ca/diesel-duck/library/articles/bulbous_bows.htm
Has Bolger ever designed a boat with a bulbous bow?
Has Bolger ever designed a boat with a bulbous bow?
> lifting over waves. Bolger also mentions it's ability to part a chopI think the box keel cheats the standard calculation of displacement
> and the fact that it doesn't push up much of a wave infront or
> behind,
hull speed a little bit, by spreading out the wave making effect of the
hull, at least when compared to conventional hulls.
[Other benefits of box keels include: Protection of the rudder,
and the providing of a stable platform for the boat to stand
upon on dry land. Also, the box provides some lateral plane.
The heavy plate on the foot, in Col. Hasler and Yonder, for instance,
provide weight down low where it is best for stability.]
IMO the keel adds
Performance wise not sure, it seems like alot of wetted surface
area. However for a small boat it gives a ton of volume up front for
lifting over waves. Bolger also mentions it's ability to part a chop
and the fact that it doesn't push up much of a wave infront or
behind, so i would think it must be pretty hydrodynamicly fit. It
allows the ballast to be low like a full/fin keel. Most importantly
on a boat like the Col. It adds an immense amount of displacement
allowing for steel construction and allows standing headroom without
all the windage of say a micro navigator.
> strength to the hull design, but I'm not sure how it would benefitinside
> performance over a conventional centerboard or lee board. From my
> point of view, it does eliminate a fragile moving part and the
> of the board housing that is difficult to maintain. Both of theseare
> of benefit for any craft.************
>
Performance wise not sure, it seems like alot of wetted surface
area. However for a small boat it gives a ton of volume up front for
lifting over waves. Bolger also mentions it's ability to part a chop
and the fact that it doesn't push up much of a wave infront or
behind, so i would think it must be pretty hydrodynamicly fit. It
allows the ballast to be low like a full/fin keel. Most importantly
on a boat like the Col. It adds an immense amount of displacement
allowing for steel construction and allows standing headroom without
all the windage of say a micro navigator.
donschultz8275
proof-of-concept design, which would be the 8ft Flying Cloud.
Hasler, of course, also has a pretty large retractable off-centerboard,
in addition to the box keel.
Where Flying Cloud relies on the lateral resistance of the box sides only.
> I had not seen Flying Cloud before. Per the essay, it is a proof ofIn the writeup to the 20ft Col. Hasler, they mention a 40%
> concept rather than a standalone new design.
proof-of-concept design, which would be the 8ft Flying Cloud.
Hasler, of course, also has a pretty large retractable off-centerboard,
in addition to the box keel.
Where Flying Cloud relies on the lateral resistance of the box sides only.
Exerpted from MAIB website; "When the hull would hit a wake from
another boat, it would plunge into it and come to a complete stop,
which could severely injure the occupants. After learning of this, I
needed to design a safe hull for those speed demons but easy to build.
I remembered my box keel boat from when I was a kid, so I de-signed my
10' and 11' tugs using a modified box keel bottom with additional aft
planing surface. Both of these boats have ride and handling
characteristics that are superb, even at speeds of 25 mph.
What goes around comes around. The box keel is back.
Berkeley A. Eastman 1640 Reche Road Fallbrook, CA 92028"
This article describes boats that sound very much like Hawkeye and
Microtrawler. Bolger shows a "yawl boat" on the deck of "Puffer", one
of his live-aboard designs very similar to the pic associated with the
essay quoted above.
The purpose of the box keel is different for planing power vs' sail
designs, thus the similarities are pretty superficial.
Common traits, in my opinion, are excellent physical strength and
durability, and good beaching qualities.
I had not seen Flying Cloud before. Per the essay, it is a proof of
concept rather than a standalone new design. IMO the keel adds
strength to the hull design, but I'm not sure how it would benefit
performance over a conventional centerboard or lee board. From my
point of view, it does eliminate a fragile moving part and the inside
of the board housing that is difficult to maintain. Both of these are
of benefit for any craft.
The benefits of adding a box keel to a simple flat bottom powered boat
are easy for me to see. Reading the essay for Hawkeye in BWAOM, makes
me want to have added a box keel to about 1/3rd of the boats I've
owned over the years. Several would have been better boats for such a
device.
another boat, it would plunge into it and come to a complete stop,
which could severely injure the occupants. After learning of this, I
needed to design a safe hull for those speed demons but easy to build.
I remembered my box keel boat from when I was a kid, so I de-signed my
10' and 11' tugs using a modified box keel bottom with additional aft
planing surface. Both of these boats have ride and handling
characteristics that are superb, even at speeds of 25 mph.
What goes around comes around. The box keel is back.
Berkeley A. Eastman 1640 Reche Road Fallbrook, CA 92028"
This article describes boats that sound very much like Hawkeye and
Microtrawler. Bolger shows a "yawl boat" on the deck of "Puffer", one
of his live-aboard designs very similar to the pic associated with the
essay quoted above.
The purpose of the box keel is different for planing power vs' sail
designs, thus the similarities are pretty superficial.
Common traits, in my opinion, are excellent physical strength and
durability, and good beaching qualities.
I had not seen Flying Cloud before. Per the essay, it is a proof of
concept rather than a standalone new design. IMO the keel adds
strength to the hull design, but I'm not sure how it would benefit
performance over a conventional centerboard or lee board. From my
point of view, it does eliminate a fragile moving part and the inside
of the board housing that is difficult to maintain. Both of these are
of benefit for any craft.
The benefits of adding a box keel to a simple flat bottom powered boat
are easy for me to see. Reading the essay for Hawkeye in BWAOM, makes
me want to have added a box keel to about 1/3rd of the boats I've
owned over the years. Several would have been better boats for such a
device.