Hull speed

[Neil Gordon]

>>OK, so a towed dinghy does create at least some drag and slow me down. If I haul it up on deck (not like there is room on a Ty) it would increase the weight of the boat, causing her to sit lower in the water, increasing the waterline and therefore increasing the hull speed, right?<<

Right... the increase would be in *theoretical* hull speed. Last I looked, it was not a common racing tactic to flood a boat to the point where the decks were awash (which would generally maximize the waterline length).


Regards, Neil
s/v LIQUIDITY
Cape Dory 28 #167



cdory28@aol.com

[matt cawthorne]

John,

but it's incredibly interesting.

If you are interested in this stuff try reading a book called "Seaworthiness, the forgotten factor" by C.A. Marchaj.

It will increase your understanding of why a hull shape like a Cape Dory is so good.

Matt



mcawthor@bellatlantic.net

[Joe Sankey]

I can't make a real contribution to this thread. However, a friend who now owns and sometimes races his CD27 used to own a CD22 at the same time I did, as well. He wins/won regularly racing Portsmouth and he told me the more you make a CD22 like "a submarine" the faster it goes. I don't think water in the bilges was what he had in mind, but he did like weight in it.
Joe Sankey
CD 30 Slow Dance

>>OK, so a towed dinghy does create at least some drag and slow me down. If I haul it up on deck (not like there is room on a Ty) it would increase the weight of the boat, causing her to sit lower in the water, increasing the waterline and therefore increasing the hull speed, right?<<

Right... the increase would be in *theoretical* hull speed. Last I looked, it was not a common racing tactic to flood a boat to the point where the decks were awash (which would generally maximize the waterline length).


Regards, Neil
s/v LIQUIDITY
Cape Dory 28 #167

sankey@gulftel.com

[John Vigor]

You'll find my book, "The Seaworthy Offshore Sailboat" (International Marine) much easier to understand. Marchaj is highly technical, and not suitable for Lancashire lads.

John Vigor
CD25D "Jabula"



jvigor@qwest.net

[John Nuttall]

Matt, John V., & Neil,

Thanks for the feedback. However I have some further questions & comments.

1)I recognize the importance of the righting moment Neil was describing in his comments about tenderness. Yes I recognize that as a factor. However that force is usually counteracted by the righting arm of the mast/force on the sails. There is an impact on tenderness as that reserve bouyancy kicks in when heeled over. Boats with vertical ends - say a Flicka - wouldn't have this effect. Do the overhangs/reserve bouyancy allow a designer to get more stability with less lead in the keel. Lighter hopefully being faster...????

2)I am aware that there is a reduction in wetted surface as CDs heel over. Ideally this would result in less drag and more speed for a given sail area. Loading up a boat with dingies or lead would lower it and increase the waterline and theoretical hull speed BUT it would also increase wetted surface & drag. This I suppose would slow it down....?

Anyway, I certianly know a boat is a "system" and everything has to be balanced and work as a whole. I guess I'll have to heed Mssr. Vigor's advice and buy his book to get my answers!!!

Cheers
John N.
s/v Aimless
CD31 #28
Oriental, NC

ps John V., What about some of the racing yachts of yore with the extremely long overhangs? Were the overhangs functional, or just some sort of rule beater design??...



aimless@nc.rr.com

[cptn seaweed]

Matt, John V., & Neil,

Thanks for the feedback. However I have some further questions & comments.

1)I recognize the importance of the righting moment Neil was describing in his comments about tenderness. Yes I recognize that as a factor. However that force is usually counteracted by the righting arm of the mast/force on the sails. There is an impact on tenderness as that reserve bouyancy kicks in when heeled over. Boats with vertical ends - say a Flicka - wouldn't have this effect. Do the overhangs/reserve bouyancy allow a designer to get more stability with less lead in the keel. Lighter hopefully being faster...????

2)I am aware that there is a reduction in wetted surface as CDs heel over. Ideally this would result in less drag and more speed for a given sail area. Loading up a boat with dingies or lead would lower it and increase the waterline and theoretical hull speed BUT it would also increase wetted surface & drag. This I suppose would slow it down....?

Anyway, I certianly know a boat is a "system" and everything has to be balanced and work as a whole. I guess I'll have to heed Mssr. Vigor's advice and buy his book to get my answers!!!

Cheers
John N.
s/v Aimless
CD31 #28
Oriental, NC

ps John V., What about some of the racing yachts of yore with the extremely long overhangs? Were the overhangs functional, or just some sort of rule beater design??...

It is my understanding that when a boat heals, it increases wetted surface. I also understand the overhangs are mostly for lift in heavy seas, especially from the stern. John CD31 #18

[cptn seaweed]

Mitch,

As I'm not a physicist either and I'm sure others will post more thorough follow-ups, however, I'll give it a shot. In regards to the hull speed, you're close but missing one part of the equation. It's the square root of the waterline multiplied by approximately 1.3. As to the dingy question, I believe most dingies would plane and would therefore only have a minimal amount of drag.

Craig Curtis
1990 CD40 "Coalescence"

If we cape dory owners were concerned about a 1/2 knot more speed we would buy a melges
John CD 31 # 18



redzeplin@yahoo.com

[John Vigor]

Mr. Nuttall:

I am distressed that you regard my contribution as shameless self promotion. If that's the feeling, I shall bother this bulletin board no more.

John Vigor
CD25D "Jabula"



jvigor@qwest.net

[Catherine Monaghan]

John, hey wait a minute. Your contributions are highly valued. Don't let a little criticism (constructive or destructive) scare you off. The rest of us would like to hear (read) what you have to offer.


catherine_monaghan@merck.com
CD32 <a href="http://www.hometown.aol.com/bcomet/real ... ization</a>, #3
CCDOA Assistant Webmaster
Rahway, NJ
Raritan Bay

Mr. Nuttall:

I am distressed that you regard my contribution as shameless self promotion. If that's the feeling, I shall bother this bulletin board no more.

John Vigor
CD25D "Jabula"

catherine_monaghan@merck.com

[Tom]

I second Catherine's motion. Mr. Vigor I have always found your posts to be some of the most informed and valuable that we get on this board and not self serving in any way. Please don't get the impression that that is the general feeling out here. In fact, I didn't think John Nuttall meant it that way. I took the original post to be tongue in cheek with the smiley face and then the additional questions.

Mr. Nuttall:

I am distressed that you regard my contribution as shameless self promotion. If that's the feeling, I shall bother this bulletin board no more.

John Vigor
CD25D "Jabula"

TomCambria@mindspring.com

[John Nuttall]

Dear Sir: ...didn't you see the "wink"... ???

As a matter of fact, I dug out my copys of Good Old Boat to find the order form for your books! ( I'd rather order from GOB - to help their cause - than some megabookstore.com )

Unless protocol calls for getting an autographed copy directly from you - to atone for my sins , so to speak. Please advise....

Anyway, I warned you about my Lancashire blood....what I didn't tell you about is the maternal side ..... pure Donegal !!! What a mongrel .....

BTW: Can you clear up my thoughts on this topic, or do I have to wait for your book?

Kindest Regards,

John Nuttall
(currently suffering with 101 degree heat in Lizard Lick, NC)

CD31 Aimless



aimless@nc.rr.com

[John Nuttall]

.... just found the ad in GOB....Mar/Apr 2001....p65...$29.95



aimless@nc.rr.com

[will parker]

I will "AMEN" that sentiment. I have read John Vigor's stuff for a long time and consider it a very valuable resource in my library. His experience is priceless and he has been willing to share it with us for nothing.
Stick around, John, we need your input!
Will
Jambalaya
CD30c


John, hey wait a minute. Your contributions are highly valued. Don't let a little criticism (constructive or destructive) scare you off. The rest of us would like to hear (read) what you have to offer.

catherine_monaghan@merck.com
CD32 <a href="http://www.hometown.aol.com/bcomet/real ... ization</a>, #3
CCDOA Assistant Webmaster
Rahway, NJ
Raritan Bay

Mr. Nuttall:

I am distressed that you regard my contribution as shameless self promotion. If that's the feeling, I shall bother this bulletin board no more.

John Vigor
CD25D "Jabula"

whildenp@flinet.com

[Will Parker]

John,
Your experience is valuable to all of us and obviously most of us appreciate your willingness to share it with us on this board. Don't let a careless comment silence you. Indeed, I couldn't believe my good fortune when I began reading your comments here. As a matter of fact, I have your book "The Seaworthy Offshore Sailboat", and I have read and re-read it and recommend it to all. I have followed you writings since your courageous and dangerous sailing departure from South Africa.
Please stick around and help us when we need it.
Thanks
Will
"Jambalaya"
CD30c

Mr. Nuttall:

I am distressed that you regard my contribution as shameless self promotion. If that's the feeling, I shall bother this bulletin board no more.

John Vigor
CD25D "Jabula"

whildenp@flinet.com

[Bob Chamberland]

Ease up folks.



cha62759@traverse.com