Full Keel Cross Section Question

[TeddyDiver]

Originally Posted by viking north

yup you're right a bloody big trail of vortex bubbles coming off the bottom of the keel, looked like white rope.
Is this a normal occurance with full keels,

If you want get rid of the bubbles have somewhat rounder leading edge on the keel and stem. That should prevent the separation of the flow and cause of the "rope". But anyway they are only bubbles..

[Lurvio]

Viking North

Would you mind posting links to the threads you've found helpful.

L

[viking north]

Well there goes another theory and I was doing so good. My reasoning was if i had to ballast her down in the stern to get cleaner water for the prop. she pivots on her midsection, the bow rises accordingly. The keel bottom which was parallel with the waterline now moves out of this relationship and effectively duplicates the drag designed keel. I do see where you are coming from in that the drag is designed into the keel initally by increasing its vertical dimension aft.---Geo

[viking north]

Lurvio, will do, have to go back to the sites, get their addresses, and then type them in here for you. Probably an easier way but I.m computer handicapped--Geo.

Teddydiver--only bubbles you say--you didn't have a monster sardine trying to pull the prop and shaft clean out of your boat -- that was the weirdest thing i've ever seen on the water.

[Lurvio]

Ctrl C --> Ctrl V (copypaste) is a friend. Click on the address bar so the text changes colour, hit Ctrl C. Then in advanced mode hit add hyperlink and hit Ctrl V.

L

[viking north]

You lost me after the smiley face second Ctrl C, what is advance mode and how do I hit and add hyperlink (sounds like the engine room of Enterprise)
My speed:
Step 1 once you have located the site click on ----------
Step 2 and so on
Don't get me wrong i want to learn the how as I can then easily use references in my posts-- the other post additive feature is transferring a quote from one post to ones own in order to reply to it -- the caveman awaits---Geo.

[viking north]

Ok Lurvio to save time got them manually (Long keel leading edges) be sure to read the reference ad. on post #7 of this thread also.
The other site all the ad. is the same up to the word design then type in /long-crusing-keel-foil-shapes-5280-2.html
Get back to me if you are unsucessful and i will check for mistakes in my reading or typing of them--Geo

Back in edit-thats weird that long address i typed in changed to a simple (Long keel Leading edges) Ok let me type in the full ad. of the second site and see what happens it might do the same. http://www.boatdesign.net/forums/boa...es-5280-2.html

Now it kept the full long address- these computers are more complicated than keel foil shape formulae- anyhow there you have them--geo

[Lurvio]

Had to go and pick up the missus from bus stop.

Thank you for the links, I think my evening program is set.


Here's a bit more detailed version of howto post links:

The commands have some variation between different browsers, these are from Mozilla Firefox. Ctrl commands (the ones listed here) are universal in most programs.

Step 1
Go to a web page you want to link to the post. Click on the address bar (might need double- or triple-click) so the text changes color ie. is selected.

Step 2
Now to copy the link to computer clipboard, method one is to click Ctrl + C (keep Ctrl down and hit C simultaneously). Other way is to click on the selected link with right mouse key and select 'copy' (or copy link) from the resulting menu.

An existing link on a webpage can be copied without visiting the linked page by mouse right click on the link and selecting 'copy link location'.

Step 3 (viking - you were in the right place as you were able to post links)
Next you go to the posting page (the advanced one, not the 'post quick reply') and hit add hyperlink button (the small planet with a chainlink). When the hyperlink box pops up, hit Ctrl + V or mouse right click and select 'Paste', the link copied earlier should now be in the box. After pressing Ok you return to the posting and part of the added text is selected (different colour), that is the part of the link that is visible in the final post and can be edited (as you allready have done)

Well, I am pretty sure i forgot something here so ask away if this did not make sence. :9

Lurvio

[PAR]

Viking, you can have your cake and eat it too. Once you've trimmed out your boat, with the butt down, which places the keel bottom bow up. Use some angle stock, just above the forward end of the keel (the high point) then trail this angle stock aft, so it mirrors the LWL. A 1" aluminum angle can be screwed to the deadwood and faired pretty easily. It would probably be better to "let" the stock into the deadwood, so fairing is minimum, but in a perfect world we'd all be married to my first wife, but with a personality.

Also, consider an end plate for your prop if it's starving. This is precisely what the anti ventilation plate, on an outboard is designed to do.

[viking north]

Par to give you some idea of what i'm working with i'm posting the build in progress on the forum under boatbuilding---"The Nancy G----" Nice symetrical hull but i have to do some changes. I've got her bare hull weight down to 3000lb, my finished displacement goal is under 10,000. I have to raise the deck edge before installing the deck, to gain headroom in the main cabin . as she sits she's 28ft.LOA, 7ft. 6in.beam and only 48in. deep midships but alot of sheer so it makes the raising by 12in not too bad by filling in the sheer. Her CB is about 1ft. aft of midship. Cp is .58 so she's got potential. I have all her hydrostatics , don't know what half of it means but it looks good. The designer is off on 2 weeks holidays so should have her lines to post when he returns. I have a few more questions on the keel but pretty well got that put to bed. I want to do a cutout in the keel but not sure if there is a ratio on the lengths of the parts ,I.E. main keel verses skeg verses cutout. Company just arrived with beer and guitars will get back to you- Have a good one--geo.

[viking north]

Ok that little birthday function is over, on with life- as I was saying the ratios of each, The more i think of it the more i think i'm overthinking, just place the Brewer style bite back far enough to leave a good solid skeg and enough cutout to allow a good cross flow to get her stern around when tacking. I'll do a scale drawing pass it on to the designer to plug it into his program and see what evolves. I'm still into the end plate idea so once i nail down a little more info on finished waterline verses the prop emersion I'm gonna get back to that. Thanks again for the help---Geo.

[PAR]

The traditional "Brewer Bite" isn't as good as a fully formed skeg. In later design, even he has abandoned the little bite in favor of a full up skeg, usually with a small bridge at the top, tieing it to the fin. End plates work good on these too.

[MikeJohns]

Scheel keels turned out to be very draggy in tank testing although they may look elegant they are not a good solution. Even Ted Brewer went to the effort of testing a Scheel keel and abandoned the idea. It turned out there are significant trailing vortices generated by the protuberances even with steady smooth sailing conditions. Then the more the boat heaves and pitches the worse the vorticity becomes.

You get a lot less vorticity (resistance) by simply widening the foil at the bottom to accommodate the ballast and if at the same time you can narrow the foil at the top you also further reduce drag.

The full keel also lends itself well to a cutout astern with a supporting heel for the rudder which can then be balanced then it acts as an independant foil rather than just altering the pressure distribution on the keel which an attached rudder does. You can shed some surface area this way. Designers like Chuck Paine have even done this recently with a raked transom hung rudder on a 45 footer I think and it apparently worked well.

[viking north]

More bubble trails astern- more whales trying to grab the ropes . Did a few more measurements and calculations today It's looking more like i will have to ballast her stern down a little so the end plate idea although a simple addition might give me more problems than good by not being in parallel with the waterline. PAR, Photo your post#12 as a reference for me i think is what Mike is now referring to. Another problem i am fighting is final displacement, I've got to keep it below 10,000lb. This hull is old style, narrow in the beam and at 4000 lb displacement she sinks 1in for every 500lb gradually topping out at 1in. for every 700lb at 10,000 displacement. My inital thinking on ballast was 4000lb. on 12000lb final displacement but when the hydrostatics came in from the designer the canoe hull would be emerged 31in, and she would draw 56in. with new 24in. dept. of keel installed. I want to keep my final draft around 48in.to accomidate half tide water dept at my marine railway. One quick way i can reduce weight is to reduce ballast to 3000lb. and a max. 10,000lb final displacement which i think was a more realistic figure anyway from the get go. Still not a bad ratio considering she is a motorsailer style ( lesser sail area). That photo and Mikes description gave me an idea that if i did go with this model my reduced ballast would be lower down and more effective, possibly just as good as the 4000 in the origional configuration. Now the big question, I understand that once again it is important to keep the longitudional run of this lower wider section parallel with the waterline, What tolerance do i have on this . Say it's out of parallel by 3 or 4 in on 10ft. will that create unacceptiable drag. ( this out of parallel would be on an upward plane toward the bow) (I.E.as if a subs. bow planes were set to surface) --- Thanks again guys for your time and interest--Geo.

[viking north]

Have done more research into this idea and now got a better drift of the possibilities. From some photos and writeups on Sheel keel copies I'm convinced that actual bolt on scheel type add on's are possible. Once the mold pattern is taken off say a full keel or a keel/skeg combination, I think it would be possible to thru bolt them to the sides of an existing keel. I could launch the boat and operate for one season with say 500lb. or so less ballast in the keel by installing internal removeable ballast. This would allow me to establish her actual operational waterline and give me a good idea of performance. From the pre launch patterns I could then make up the wing like sections , bolt them in place and compare. Meanwhile It allows me to go forward with construction on a straight forward keel/skeg combination. What think ye ? One can have fun if it's one's own boat--Geo.

A yacht is not defined by the vessel but by the care and love of her owner.