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Jerryd

Rocket Keel

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While I have the Rocket off the trailer to clean up and fair the keel, I thought it would be a good time to lob off about 10" to make it more draft friendly for these parts. I mean, what's 10 inches B)

post-42193-0-11396100-1351709767_thumb.jpg

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thats the difference between oh and OOOOOOOOOHHHHHHHHHH

 

 

How much weight is in the bulb?

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Bulb is like 700-800 pounds. I had a Rocket, I think you might be able to move the wedge things from the top of the keel down a ways and it would still lock in so you could still drop it to full depth when needed. It would be a bit of a pain to get below though.

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what number Rocket you have? We took 200lbs off number 1's bulb to get it down to class weight, sails just like a infused boat now!

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what number Rocket you have? We took 200lbs off number 1's bulb to get it down to class weight, sails just like a infused boat now!

 

I heard about that but didn't know how to reach you. Hull #6 here. Not infused obviously. I think Betts did yours? I've tried to reach him numerous times without any luck. I wanted to see what the profile looked liked after the trim? Did it come off the length or diameter or both? How much trimming was needed?

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Jim Betts did the work and was bloody great to be honist, they took the weight off the sides and bottom removing the fattest part. It has made a huge diffrence to the boats down wind performance and has not really effected the upwind. That said we did a lot of much needed maintainance at the time, cleaned up the foils etc, but the bottom line is the original prototype is now compeditive with the lightest Rocket made and can race boat for boat. Another big change we made was to go to a square top main, The foot was reduced by a foot so we did not take a headboard hit under PHRF, infact we got a 3 second increase. The boat tacks much better in higher breeze and has a better balance overall.

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Jim Betts did the work and was bloody great to be honist, they took the weight off the sides and bottom removing the fattest part. It has made a huge diffrence to the boats down wind performance and has not really effected the upwind. That said we did a lot of much needed maintainance at the time, cleaned up the foils etc, but the bottom line is the original prototype is now compeditive with the lightest Rocket made and can race boat for boat. Another big change we made was to go to a square top main, The foot was reduced by a foot so we did not take a headboard hit under PHRF, infact we got a 3 second increase. The boat tacks much better in higher breeze and has a better balance overall.

Before and after pics or it didn't happen...

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Jim Betts did the work and was bloody great to be honist, they took the weight off the sides and bottom removing the fattest part. It has made a huge diffrence to the boats down wind performance and has not really effected the upwind. That said we did a lot of much needed maintainance at the time, cleaned up the foils etc, but the bottom line is the original prototype is now compeditive with the lightest Rocket made and can race boat for boat. Another big change we made was to go to a square top main, The foot was reduced by a foot so we did not take a headboard hit under PHRF, infact we got a 3 second increase. The boat tacks much better in higher breeze and has a better balance overall.

 

Yeah, pics please!

 

I may do the bulb while we have it off the trailer. It would be great to have a picture of yours for some guidance for the yard. I have a square top on order from Ullman as well as a new cassette style rudder from Phil's. Also changed the traveler line by removing it from the center console and running along the inside of the cockpit to cleats next to the driver.

 

 

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?

an infused boat is lighter ?

 

I know things are different downunder but we could not effectively 'work' a trav with cleats inside the cockpit

 

why not just race the boat fer starters

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?

an infused boat is lighter ?

 

I know things are different downunder but we could not effectively 'work' a trav with cleats inside the cockpit

 

why not just race the boat fer starters

 

Early boats like mine were vacuum bagged and around 200 lbs heavier then the infused hulls which do a better job and reducing excess resin.

 

Cleats for the traveler line inside the cockpit are unusual? Think Melges 24, J-80, etc., etc. If you saw how the stock setup works you wouldn't question it at all! The stock setup has a continuous travel line that goes through the center control console where it can be cleated from either side. From there it goes down and inside under the cockpit around several blocks and then comes back up at the end of the traveler track. Lot's or turns and lots of friction!

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?

an infused boat is lighter ?

 

 

Early boats like mine were vacuum bagged and around 200 lbs heavier then the infused hulls which do a better job and reducing excess resin.

 

 

Also, infused laminates can skip the intermediate binding mat layers that poly & vinyl ester "wet" layups need to guard against de-lamination. That in itself drops a lot of weight from your composite parts. Mat has a very low strength to weight ratio.

 

I remember Betts doing all sorts of hacking and chopping on your rocket.

 

-jim lee

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?

an infused boat is lighter ?

 

 

Early boats like mine were vacuum bagged and around 200 lbs heavier then the infused hulls which do a better job and reducing excess resin.

 

 

Also, infused laminates can skip the intermediate binding mat layers that poly & vinyl ester "wet" layups need to guard against de-lamination. That in itself drops a lot of weight from your composite parts. Mat has a very low strength to weight ratio.

 

I remember Betts doing all sorts of hacking and chopping on your rocket.

 

-jim lee

 

Not mine. That was lowcamaro. Hull #1. From what I understand, they reduced the weight to get down simillar to a infused hull by reducing the bulb diameter and taking out the additional 200 lbs. Something I'm thinking about.

 

Jim, I notice that your bulb doesn't come to a point in the back but rather a horizontal flat tail. At least that's how it looks in the build pictures. Is there some science to that shape?

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Oh I though that was your rocket, Sorry.

 

As for my keel end.. I asked Leif about the keel shape once. Its actually really complicated with subtile curves and all that. It was a real nightmare to get right. But I digress.. After busting tail to get the silly thing right, I asked leif why the shape was so critical and where it came from. He went on for a long time about this that and the other, at one point it was linked to French wine in some obscure way. Nevertheless, I couldn't follow him at all. I suspect he thought it looked cool or something. I have no idea.

 

-jim lee

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Oh I though that was your rocket, Sorry.

 

As for my keel end.. I asked Leif about the keel shape once. Its actually really complicated with subtile curves and all that. It was a real nightmare to get right. But I digress.. After busting tail to get the silly thing right, I asked leif why the shape was so critical and where it came from. He went on for a long time about this that and the other, at one point it was linked to French wine in some obscure way. Nevertheless, I couldn't follow him at all. I suspect he thought it looked cool or something. I have no idea.

 

-jim lee

 

Thanks! . I guess as we slim down the bulb, we'll keep the pointed end unless someone comes up with a bettter reason not to :rolleyes:

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Is there some science to that shape?

 

of course it has to do with vortices, it's an end-plate

 

without the science, from a back yard (man with a powerplane technology) angle the fastest you aim for is the least frontal area, that is it would punch the smallest hole through a plasticine wall, thats what's happening with the latest designs anyway

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Actually, although I don't know why bulbs are shaped as they are, it was important enough for Leif to design ours so that the shape is molded into the glass. This way it can be repeated to a tight tolerance on each boat. This tells me that the shape was more important than the CG lost in an encapsulated ballast design.

 

I guess he was right, boat seems to sail fine..

 

-jim lee

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I was in the shop for the first six rockets,,doing smallparts ,some assembly,,and what for the time was custom work.

....the layup guys were nice folks and all,,,but yer couldn't do -anything- to stop them from brushing extra resin on everything,all the time.....paranoid of dry layup.

 

....the core was vacuumed to the outside skin,,otherwise everything was very wet layup

 

...I believe the bulbs were all close to 680 lbs iirc

 

.........sorry about the rudders---doing whut I was told <_<

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I was in the shop for the first six rockets,,doing smallparts ,some assembly,,and what for the time was custom work.

....the layup guys were nice folks and all,,,but yer couldn't do -anything- to stop them from brushing extra resin on everything,all the time.....paranoid of dry layup.

 

....the core was vacuumed to the outside skin,,otherwise everything was very wet layup

 

...I believe the bulbs were all close to 680 lbs iirc

 

.........sorry about the rudders---doing whut I was told <_<

 

Thanks for the feedback?

 

I thought the bulbs were more like 800 lbs?

 

Funny, I've seen reference to the rudder being 15lbs. If they're 15 lbs! I've got to get in to the gym more often! I ordered a new cassette style rudder from Phil's foils which will make it a lot easier.

 

GS- I like the "Powerplane Technology" !

 

GS-

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Oh I though that was your rocket, Sorry.

 

As for my keel end.. I asked Leif about the keel shape once. Its actually really complicated with subtile curves and all that. It was a real nightmare to get right. But I digress.. After busting tail to get the silly thing right, I asked leif why the shape was so critical and where it came from. He went on for a long time about this that and the other, at one point it was linked to French wine in some obscure way. Nevertheless, I couldn't follow him at all. I suspect he thought it looked cool or something. I have no idea.

 

-jim lee

 

"Any scientist who can't explain what he's doing to a six-year-old is a charlatan." -Kurt Vonnegut

 

I have found that to be very good advice. I would include high-level engineering design.

 

FB- Doug

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I was in the shop for the first six rockets,,doing smallparts ,some assembly,,and what for the time was custom work.

....the layup guys were nice folks and all,,,but yer couldn't do -anything- to stop them from brushing extra resin on everything,all the time.....paranoid of dry layup.

 

....the core was vacuumed to the outside skin,,otherwise everything was very wet layup

 

...I believe the bulbs were all close to 680 lbs iirc

 

.........sorry about the rudders---doing whut I was told <_<

 

Thanks for the feedback?

 

I thought the bulbs were more like 800 lbs?

 

Funny, I've seen reference to the rudder being 15lbs. If they're 15 lbs! I've got to get in to the gym more often! I ordered a new cassette style rudder from Phil's foils which will make it a lot easier.

 

GS- I like the "Powerplane Technology" !

 

GS-

 

....it's been awhile,,,but methinks the foil/bulb came to 800something pounds.

 

....rudders at 15lbs?...not in the first 6 certainly.....I can't image those lasted long anyways,let alone the wavy moulds(?)

..........there wasn't really anything that was being spec'd to weight to begin with except the finn/bulb

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Sail the boat for a season first. Shortening the keel is going to do you no favors, nevermind that it will F your resale.

 

If you do need to do it, plutos idea is not bad, move the wedges down and create an intermediate end plate around the foil without shortening it.

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Sail the boat for a season first. Shortening the keel is going to do you no favors, nevermind that it will F your resale.

 

If you do need to do it, plutos idea is not bad, move the wedges down and create an intermediate end plate around the foil without shortening it.

 

 

...I -was- going to suggest being careful to not drill through the threaded rod that runs through the foil,,

,,,but remembered the threaded rod is -only- at the ends............which brings up another possible concern of longevity....

 

.....anyone know the service life of cast aluminum in that application?

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was he serious about shortening the fin

 

that will be a $6000 cut (or whatever a new fin will cost) , better to wedge it up & thru bolt, can't have it moving around at plus 90^.

 

also you would not (both) shorten fin and reduce the bulb weight if there was any serious breeze on the horizon, that would be a double (& compounding) whammy

 

Lucky the rocket gets a large portion of its RM from it's wiiiiide hull form, that does give alot of scope here, and is the main (only) reason you can play at the keel weight/depth

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"Any scientist who can't explain what he's doing to a six-year-old is a charlatan." -Kurt Vonnegut

 

I have found that to be very good advice. I would include high-level engineering design.

 

FB- Doug

 

I didn't know Vonnegut said that, but it is SOOO true!!

 

I think Lief was more about not letting on than not knowing. Good lord I hope! :)

 

-jim lee

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Sail the boat for a season first. Shortening the keel is going to do you no favors, nevermind that it will F your resale.

 

If you do need to do it, plutos idea is not bad, move the wedges down and create an intermediate end plate around the foil without shorteninged it.

 

No worries Chris. I wasn't planning on cutting it short. Possibly modifying it to be pinned or wedged in a higher position. Right now I'm more interested in pulling some of the weight out of it via the bulb like #1 did.

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well what are you racing it against ?

 

could be a folly if you REALLY envisage sailing 'shallower draft'

 

are you in a light weather area ?

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"Any scientist who can't explain what he's doing to a six-year-old is a charlatan." -Kurt Vonnegut

 

I have found that to be very good advice. I would include high-level engineering design.

 

FB- Doug

 

I didn't know Vonnegut said that, but it is SOOO true!!

 

I think Lief was more about not letting on than not knowing. Good lord I hope! :)

 

-jim lee

 

Oh, I think he's a pretty smart designer. Not trying to show a big hate-on like many here at SA. But explaining the advantages of one keel design over other variations ought to be pretty straightforward. He may have been trying to fancy up words to the effect "it's a lot better than the B-25" which of course it is.

 

FB- Doug

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It would sure be nice to get a few tips from the experts. My guy at the boat yard has a power planner in hand and is ready to fire it up once I give them some direction ;)

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It would sure be nice to get a few tips from the experts. My guy at the boat yard has a power planner in hand and is ready to fire it up once I give them some direction ;)

 

.....you can only get ~3/8-1/2'' off the bottom of the bulb before the keelbolts will be in the way.

and iirc the keel's more flattish on the bottom already(?)

 

....probably best to skinny the sides would give you the best and simplest outcome

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It would sure be nice to get a few tips from the experts. My guy at the boat yard has a power planner in hand and is ready to fire it up once I give them some direction ;)

 

.....you can only get ~3/8-1/2'' off the bottom of the bulb before the keelbolts will be in the way.

and iirc the keel's more flattish on the bottom already(?)

 

....probably best to skinny the sides would give you the best and simplest outcome

 

We've already exposed the keel bolts so we knew were they were. The plan was to take off some of the fat sides. The power planner isn't working well. Chain saw next :blink:

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It would sure be nice to get a few tips from the experts. My guy at the boat yard has a power planner in hand and is ready to fire it up once I give them some direction ;)

 

.....you can only get ~3/8-1/2'' off the bottom of the bulb before the keelbolts will be in the way.

and iirc the keel's more flattish on the bottom already(?)

 

....probably best to skinny the sides would give you the best and simplest outcome

 

We've already exposed the keel bolts so we knew were they were. The plan was to take off some of the fat sides. The power planner isn't working well. Chain saw next :blink:

 

 

 

:blink: :blink: :blink: .........I guess if the guy's an -artist- with a chainsaw---maybe get him to do a demo in wood first...........

 

 

 

post-3217-0-51847200-1352248136.jpgpost-3217-0-51847200-1352248136.jpg

 

.

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last keel i saw done was a 60 footers weighing literally tons

 

237 kg of shavings carted away in wheelbarrows, how can a powerplane not work ?

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Beavertail bulbs are better than pointy tail bulbs because the pressure recovery is less severe so the boundary layer is better behaved hence less drag.

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Beavertail bulbs are better than pointy tail bulbs because the pressure recovery is less severe so the boundary layer is better behaved hence less drag.

 

Could be, I'm no expert. But if so, why are they never seen on sport boats?

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Beavertail bulbs are better than pointy tail bulbs because the pressure recovery is less severe so the boundary layer is better behaved hence less drag.

 

Could be, I'm no expert. But if so, why are they never seen on sport boats?

 

I believe a number of sportboats do have beavertail bulbs.

The trade-off is cross-secion vs surface area vs energy recovery

 

Winglets are the best at energy recovery, but add a lot of surface area and make the cross-section less effective

A spherical bulb has the lowest surface area for it's mass

A long skinny bulb has the least cross-sectional area for it's mass

 

To look for the best compromise, the question is- How fast does the boat go? How much do you need the bulb to help the foil? How much do you want to brag about having the highest-tech keel bulb shape in the neighborhood?

 

There's always a bit of art to the science of figuring this stuff out. One reason why sailboats are so damn fascinating.

 

If you're shaving off bulb around the middle, you are reducing the mass but also reducing surface area (to a lesser extent) and you'll end up with less surface area than you started with anyway. The cross-section will be smaller & more effective. IMHO the question is how to figure out the amount to shave off to reach your target weight. You could get fancy and beavertail it but the question is, is that going to help any with windward performance or just look cool?

 

FB- Doug

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Could be, I'm no expert. But if so, why are they never seen on sport boats?

 

Probably because the plugs are made on wood working lathes.

 

Most sports boats are designed by small design offices who can't afford top level CFD software or the computers to run it and even when you have the software there is no clear "perfect" solution. Check out the range of shapes on AC boat's keels back when they carried lead.

 

KeelComparison.jpg

 

In the absence of computer and/or tank testing optimisation, most designers will settle for trying to find the right trade off between, frontal area, Wetted surface, pressure recovery, VCG and buildability and it is not uncommon for the hours spent doing this to be thrown out because the builder has access to a bulb mould that is a different shape or because he has his own idea based upon how he wants to build it or from something he saw on the net.

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Could be, I'm no expert. But if so, why are they never seen on sport boats?

 

Probably because the plugs are made on wood working lathes.

 

Most sports boats are designed by small design offices who can't afford top level CFD software or the computers to run it and even when you have the software there is no clear "perfect" solution. Check out the range of shapes on AC boat's keels back when they carried lead.

 

KeelComparison.jpg

 

In the absence of computer and/or tank testing optimisation, most designers will settle for trying to find the right trade off between, frontal area, Wetted surface, pressure recovery, VCG and buildability and it is not uncommon for the hours spent doing this to be thrown out because the builder has access to a bulb mould that is a different shape or because he has his own idea based upon how he wants to build it or from something he saw on the net.

 

 

 

 

...ironically,,,don martin was just back from being a technical measurer at that AC about when he designed that bulb shape...jus'sayin! :rolleyes:

 

.....the shape is somewhat rounder on the upside-I suppose that'd give some lift to the bulb when the boats planing. ..I can't imagine you'll be doing much to the top or bottom since it'd add a few more challenges for your yard guy......I'd suggest you make a fairly small enclosure for grinding the lead so the lead shot doesn't surprise someone 40 feet away :blink:

 

....I can confirm the bulb-weight on those first 6 boats was pretty close to 680lbs

 

 

 

.

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...ironically,,,don martin was just back from being a technical measurer at that AC about when he designed that bulb shape...jus'sayin! :rolleyes:

 

.....the shape is somewhat rounder on the upside-I suppose that'd give some lift to the bulb when the boats planing. ..I can't imagine you'll be doing much to the top or bottom since it'd add a few more challenges for your yard guy......I'd suggest you make a fairly small enclosure for grinding the lead so the lead shot doesn't surprise someone 40 feet away :blink:

 

....I can confirm the bulb-weight on those first 6 boats was pretty close to 680lbs

 

 

 

.

 

I think we're just going to leave it alone right now and fair it out. After pulling the cauk out between the bulb and keel we have about 1/8" gap and can physically wobble the bulb while holding the keel. I'm thinking we should try to torque up the bolds to snug it to the keel and fair out the joint. Not sure how it was donein the factory?

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...ironically,,,don martin was just back from being a technical measurer at that AC about when he designed that bulb shape...jus'sayin! :rolleyes:

 

.....the shape is somewhat rounder on the upside-I suppose that'd give some lift to the bulb when the boats planing. ..I can't imagine you'll be doing much to the top or bottom since it'd add a few more challenges for your yard guy......I'd suggest you make a fairly small enclosure for grinding the lead so the lead shot doesn't surprise someone 40 feet away :blink:

 

....I can confirm the bulb-weight on those first 6 boats was pretty close to 680lbs

 

 

 

.

 

I think we're just going to leave it alone right now and fair it out. After pulling the cauk out between the bulb and keel we have about 1/8" gap and can physically wobble the bulb while holding the keel. I'm thinking we should try to torque up the bolds to snug it to the keel and fair out the joint. Not sure how it was donein the factory?

 

...I'm pretty sure that would have been 5200 at the joint,,,bolts tightened down.

 

...how easy was it to pull-out that 'caulking'?? :mellow:

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