[bolger] Re: Shrinking Martha Jane
Greg, I've been thinking about the discussion on fairing the bottom of your
Sneakeasy. I forget who, but someone mentioned that they only got about a 1/2
knot increase in speed out of it...
This was on a racing sailboat, probably already going pretty close to hull speed.
A small increase in speed close to hull speed requires a LOT of power. If they
got this from fairing the hull then there was a significant decrease in
resistance.
Also, it's my understanding that within limits power/speed on a planing hull is
relatively linear. A 15 % increase in power (or decrease in resistance) should
give about a 15% increase in speed...
Bottom line, I would guess that a 1/2 knot speed increase in a displacement hull
close to hull speed gained by fairing the hull would equate to several knots in
the Sneakeasy...
Just my 2 cents.
GHC wrote:
Sneakeasy. I forget who, but someone mentioned that they only got about a 1/2
knot increase in speed out of it...
This was on a racing sailboat, probably already going pretty close to hull speed.
A small increase in speed close to hull speed requires a LOT of power. If they
got this from fairing the hull then there was a significant decrease in
resistance.
Also, it's my understanding that within limits power/speed on a planing hull is
relatively linear. A 15 % increase in power (or decrease in resistance) should
give about a 15% increase in speed...
Bottom line, I would guess that a 1/2 knot speed increase in a displacement hull
close to hull speed gained by fairing the hull would equate to several knots in
the Sneakeasy...
Just my 2 cents.
GHC wrote:
> 15% is about the limit before you get worried. I had a problem with my
> freeboard being too low in scaling down my whitehall dory - but it's pretty
> low on that boat, anyway.
>
> Gregg
>
> At 08:31 AM 8/27/1999 -0500, you wrote:
> >The general concensus on rec.boats.building is that it's not good to
> >change the size of a boat very much, that it is much better to look for
> >another
> >design in the size you want.
> >
> >That said, all kinds of ratios change. You would probably need to look at
> >freeboard, rocker,
> >beam, and sail/board area. When you rescale something, the surface area
> >changes at the square, and the volume changes at the cube.
> >
> >Probably the best bet would be to write bolger and ask him. Also, out of the
> >hundreds of designs he has, he may have one you like in the size range you
> >are looking for.
> >
> >kahtola@...wrote:
> >
> >> Hi!
> >>
> >> Martha Jane looks like a very nice boat, but is a bit too large.
> >> I have been thinking, if it could be made a little smaller.
> >> 15% smaller might be enough. It's lenght would be ~7 metres --> ~6
> >> metres,
> >> and it's beam 1,80 metres --> ~1,5 metres.
> >> What do you think? Is it possible to do, and what should be considered
> >> specially? Could it also be made 9 mm plywood instead of 12 mm?
> >>
> >> Cheers,
> >> Teppo Kahtola
> >>
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> >>
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> >
> >
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> >
> >
> >
> >
> >
>
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>
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15% is about the limit before you get worried. I had a problem with my
freeboard being too low in scaling down my whitehall dory - but it's pretty
low on that boat, anyway.
Gregg
At 08:31 AM 8/27/1999 -0500, you wrote:
freeboard being too low in scaling down my whitehall dory - but it's pretty
low on that boat, anyway.
Gregg
At 08:31 AM 8/27/1999 -0500, you wrote:
>The general concensus on rec.boats.building is that it's not good to
>change the size of a boat very much, that it is much better to look for
>another
>design in the size you want.
>
>That said, all kinds of ratios change. You would probably need to look at
>freeboard, rocker,
>beam, and sail/board area. When you rescale something, the surface area
>changes at the square, and the volume changes at the cube.
>
>Probably the best bet would be to write bolger and ask him. Also, out of the
>hundreds of designs he has, he may have one you like in the size range you
>are looking for.
>
>kahtola@...wrote:
>
>> Hi!
>>
>> Martha Jane looks like a very nice boat, but is a bit too large.
>> I have been thinking, if it could be made a little smaller.
>> 15% smaller might be enough. It's lenght would be ~7 metres --> ~6
>> metres,
>> and it's beam 1,80 metres --> ~1,5 metres.
>> What do you think? Is it possible to do, and what should be considered
>> specially? Could it also be made 9 mm plywood instead of 12 mm?
>>
>> Cheers,
>> Teppo Kahtola
>>
>> ------------------------------------------------------------------------
>>
>> eGroups.com home:http://www.egroups.com/group/bolger
>>http://www.egroups.com- Simplifying group communications
>
>
>------------------------------------------------------------------------
>
>eGroups.com home:http://www.egroups.com/group/bolger
>http://www.egroups.com- Simplifying group communications
>
>
>
>
>
The general concensus on rec.boats.building is that it's not good to
change the size of a boat very much, that it is much better to look for
another
design in the size you want.
That said, all kinds of ratios change. You would probably need to look at
freeboard, rocker,
beam, and sail/board area. When you rescale something, the surface area
changes at the square, and the volume changes at the cube.
Probably the best bet would be to write bolger and ask him. Also, out of the
hundreds of designs he has, he may have one you like in the size range you
are looking for.
kahtola@...wrote:
change the size of a boat very much, that it is much better to look for
another
design in the size you want.
That said, all kinds of ratios change. You would probably need to look at
freeboard, rocker,
beam, and sail/board area. When you rescale something, the surface area
changes at the square, and the volume changes at the cube.
Probably the best bet would be to write bolger and ask him. Also, out of the
hundreds of designs he has, he may have one you like in the size range you
are looking for.
kahtola@...wrote:
> Hi!
>
> Martha Jane looks like a very nice boat, but is a bit too large.
> I have been thinking, if it could be made a little smaller.
> 15% smaller might be enough. It's lenght would be ~7 metres --> ~6
> metres,
> and it's beam 1,80 metres --> ~1,5 metres.
> What do you think? Is it possible to do, and what should be considered
> specially? Could it also be made 9 mm plywood instead of 12 mm?
>
> Cheers,
> Teppo Kahtola
>
> ------------------------------------------------------------------------
>
> eGroups.com home:http://www.egroups.com/group/bolger
>http://www.egroups.com- Simplifying group communications
Hi!
Martha Jane looks like a very nice boat, but is a bit too large.
I have been thinking, if it could be made a little smaller.
15% smaller might be enough. It's lenght would be ~7 metres --> ~6
metres,
and it's beam 1,80 metres --> ~1,5 metres.
What do you think? Is it possible to do, and what should be considered
specially? Could it also be made 9 mm plywood instead of 12 mm?
Cheers,
Teppo Kahtola
Martha Jane looks like a very nice boat, but is a bit too large.
I have been thinking, if it could be made a little smaller.
15% smaller might be enough. It's lenght would be ~7 metres --> ~6
metres,
and it's beam 1,80 metres --> ~1,5 metres.
What do you think? Is it possible to do, and what should be considered
specially? Could it also be made 9 mm plywood instead of 12 mm?
Cheers,
Teppo Kahtola