Cav Plate questions..

[RiverDave]

Racey, I'm getting ready to build a set of pretty decent sized cav plates for the ole Spectra over here. I had a quick question for ya.. Do you guys have a generalized "design" for the larger I/O style cav plates? Or do you make each set one off? I'm not doing the full ski race style setup with the 2 smaller inner cav plates, and 2 larger stabilization plates (for lack of a better term). I'm just doing 2 large cav plates on either side of the I/O. So now comes the 2nd question.. How big is too big? How do you determine the length / width of a cav plate? I'm assuming the longer it is, the less you'll have to move it, but the more pressure will be on the pedal's.. I'm ok with that as I'm building a hydrualic assist (powersteering pump driven) kinda setup.

RD

[Racey]

The longer the better up until a certain point when it just would become ridiculous, I would start at about 15" length on the outside edge at least, and come all the way to the center, then cut out everything for your drive clearence, i would probably do a mockup in plexigass/lexan/masonite, any cheap material that can easily be marked and jigsawed to give you proper fit to make your template then transfer it to aluminum.

You probably want something like this when you are done, maybe a little shorter i'm guessing. I think these pictured below may be closer to 18 or 20 inches long.
http://raceyindustries.com/Projects/Schiada_22IO/images/large/DSC00537.JPG




You mentioned doing a hydraulic foot pedal overide, i'd like to pick your brain on what setup you are using, i've always wanted to do that but never took the time to investigate what type of hydraulic master/slave cylinders to use, I'd like to put on in the sr-22 since it's only on an electric actuator and putting in standard foot overrides means cutting out the floors to put in all the rod linkage etc.

[RiverDave]

I was going to start at 15 - 16 inches as a guess point. I had the trailer made with 20 inch extensions on it becuase I didn't know where I'd end up.

2nd question, being that this boat is already built, and has no cav plate recesses.. Would you A : Go right off the transom with some sort of pillow block deal that spans the plate and flush mounts it? Filling the little gap with silicone / epoxy or the like (Let me know if I'm not clear on that). Or B : Grind in recesses into the bottom of the boat for a traditional mount.

If B how is that done exactly? And how do you know if the keel is thick enough that you won't run into problems down the road?

RD

[Racey]

Use a router with a straight cut single flute carbide bit to cut the recess, about 2.5" deep from the transom, and about 0.030"-0.060" deeper than the material you will use, to make room for the marine-tex epoxy, i would recommend 3/8" material for that size of plates, but you could get away with 5/16 probably, i always like to be on the heavier side.

I would say that you want about, and probably no less than 1/2" of glass after you cut the recess at the point where the bolts will go through, you can always lay in some more glass and resin inside the boat. using a complete sandwich plate instead of individual washers on each bolt will allow for a slightly thinner layup

[RiverDave]

Ok here's a question of the day..

Anyway (without drilling a hole in the bottom of the boat) to determine keel thickness? Or am I pretty much drilling it to find out? LOL

2ndly, even if I lay new glass on the inside, there's going to be areas around underneath the stringers etc.. that I'm not going to be able to get too. If the keel is say 1/2 inch to 3/4 of an inch thick, and I go cutting 3/8ths out of it.. Will the new glass really have that good of a bond to the original to make it behave like one solid part originally? (poor wording there but I think you know what I mean)

I'm just worried about cutting in, and weakening the bottom of the boat.. Then having the new glass seperate and going down with the ship in the middle of nowhere somewhere.. LOL

RD

[lebel409]

Unless the resin is still soft, the only bond that can be formed glass on glass is mechanical. So 40 grit it to give the new glass something to stick to.

Maybe some gussets from the transom to the bottom in between the stringers while the glass and resin are out? Keep the flex in check...

I'm all over over-engineerining...:beer

[stokerwhore]

there's one kind of resin,too that works good for bonding new to old.i think it's "bonding resin". others have told me it's that or nothing. i'd like to know what the technical name for this type is. does this sound right? anyone got an answer? i got some minoer delamination going on in the stoker and i've been told someone used the wrong resin to"flow coat" the inside undernieth the motor(bilge) area.

[JBB]

You know I have heard that too....I am no expert...but I have bonded alot of stuff into boats......I have used West System epoxy..(My Favorite...no smell, very strong)...and I have used numerous brands of Polyester resin...including general purpose resin.....and nothing has ever let go that I did...just buy it right before you intend to use it..(polyester) the hardener...MEKP will go bad after a fairly short time....3 mo.

look here (http://www.jamestowndistributors.com/userportal/search_subCategory.do?categoryName=Polyester%20Res in&categoryId=508&refine=1&page=GRID)

[Racey]

Rough grit the hell out of whatever area you are going to add resin and glass to 36 grit or something close, this also gets rid of any surfacing agent (usually the final layer of resin applied especially in a flow coat has a wax surfacing agent added to it which stops the resin from getting sticky again if it comes in contact with a solvent like aceton after it has dried. When adding in structure we usually will layer it up with 1 layer of matt first, then a layer of roving (sp? wide weave glass) then another matt, then a cloth on the top to finish it out. Use good resin, we like vinyl-ester (it's more expensive but really seems to work well) and i believe it bonds to all other types of resin, maybe someone else knows for sure, as most of the boats we have been doing any glass work on in the last 5 years have been vinyl-ester based anyway.

[Flat Broke]

Dave,

Out of curiosity, how come you're not looking at doing more of a tab than a plate? Somethin like you see on the big HP/#6 dealios that you'll see come out of GT on a Hallet 210, Vector, etc? I know you like the plates and all, but you can do a hinged tab and still actuate it like a traditional cav setup. I've probably got some pics of Orangepickers 210 if you're fuzy on what I'm trying to describe.

You could also hit up Mike at Rex as Shelby's Vector had a simiar setup that he made.

On the Spectra 20s that I've had my hands on (all jets mind you) the hull was about an inch thick just forward of the transom, then started tapering down, but even by the front of the intake was still pretty thick by the front of the intake hole at the keel.

If you don't want to do the routing on the bottom of the boat, I know of the pillow block setup you speak of. About the only thing I think you may need to address is the distance the block sits off the transom compared to some of the setups seen on the circle jets they're commonly found on. I think you're looking at slightly longer plates, so you may want to run a slightly deeper pillow block. I don't really see any reason why this setup would be that bad of a deal. If it's done right and tight (which I'm sure it will be if you decide to go that route), there shouldn't be much difference between doing it that way vs. the standard recess in terms of turbulence under the boat. I'd love to hear from Racey or others that have first hand experience on these type of installs vs. the standard recess version as I'm just speculating based on pictures I've seen, and that's no replacement for first hand experience.

If you need pics of pillow block based setups, I have some of Jack's personal Liberty that Mike F sent me a while ago, as well as some stuff I shot at the races when I was looking into building a set. (not that I have given up on the idea).

Chris

[River]

These might be easier?..

[scjohn]

Racey - Please excuse my ignorance on this subject. What are the advantages of cav plates over a nice set of trim tabs? What are the advantages of a cav plate set-up on an outdrive boat? What is the function of the inner and outer cav plates on a set-up like the one above? Why is the term "cavitation used to describe the plate system? Do they cause cavitation at the transom? If so what do you gain from cavitation behind the boat? Why do some mount trim tabs horizontally and others mount at the same angle as the bottom? How much movement up and down do the cav plates have? What is the advantage of the cav plates being mounted to the botton vs. hinged on the transom? Sorry for all the questions, I will be starting a new build soon maybe a Schiada 24 or 21 RC or a Hallett Vector or 210 laid up heavy for a smooth ride. I will be running a Bravo set-up with 600-700 HP.

Where did you take 2' out of the 24 Schiada you are calling SR22? It's tough to tell from the photos? How does it do on a windy day at Mead through the narrows and across the Basin headed to Big Sandy Beach?

Thanks for your help?

[RiverDave]

Dave,

Out of curiosity, how come you're not looking at doing more of a tab than a plate? Somethin like you see on the big HP/#6 dealios that you'll see come out of GT on a Hallet 210, Vector, etc? I know you like the plates and all, but you can do a hinged tab and still actuate it like a traditional cav setup. I've probably got some pics of Orangepickers 210 if you're fuzy on what I'm trying to describe.

You could also hit up Mike at Rex as Shelby's Vector had a simiar setup that he made.

On the Spectra 20s that I've had my hands on (all jets mind you) the hull was about an inch thick just forward of the transom, then started tapering down, but even by the front of the intake was still pretty thick by the front of the intake hole at the keel.

If you don't want to do the routing on the bottom of the boat, I know of the pillow block setup you speak of. About the only thing I think you may need to address is the distance the block sits off the transom compared to some of the setups seen on the circle jets they're commonly found on. I think you're looking at slightly longer plates, so you may want to run a slightly deeper pillow block. I don't really see any reason why this setup would be that bad of a deal. If it's done right and tight (which I'm sure it will be if you decide to go that route), there shouldn't be much difference between doing it that way vs. the standard recess in terms of turbulence under the boat. I'd love to hear from Racey or others that have first hand experience on these type of installs vs. the standard recess version as I'm just speculating based on pictures I've seen, and that's no replacement for first hand experience.

If you need pics of pillow block based setups, I have some of Jack's personal Liberty that Mike F sent me a while ago, as well as some stuff I shot at the races when I was looking into building a set. (not that I have given up on the idea).

Chris


Chris I thought about doing the GT Style plates, but truth be told there a little much for what we're gonna be doing with this Spectra.. (I.E. 2 sets, inner and outer etc..)

To be quite honest as far as Tabs vs Cav Plates, I can't in the world imagine why anybody would want a tab over a Cav Plate? By Hinging it your having an abrupt change in water flow (more drag, less lift) then you are with a Cav Plate.. You can move the cav plate considerably less and get = or better results.. yada yada yada.. LOL

That and lets be honest here, making a cav plate is exponentially easier then making a bitchen Hinged setup. ;)

RD

[RiverDave]

I'm not speaking for Racey here, but I figured I'd drop my .02 while your waiting on him.

Racey - Please excuse my ignorance on this subject. What are the advantages of cav plates over a nice set of trim tabs?

Less Drag = more performance. Cav plates are more "fine tuneable" then a set of Tabs.. When you lower a cav plate your essentially adding some hook to the bottom of the boat. When you lower a Tab your basically sticking a big plank down into the water = shit load of drag, to create some lift.


What are the advantages of a cav plate set-up on an outdrive boat?

Well this is gonna get kinda out there, but in the extremes it's true. Cav plates can actually add some possitive trim to the boat. If you raise them above water line, then can actually provide some bow lift. If you can raise the boat up slightly using less trim with the I/O, then your thrust direction would be more parallel to the direction of travel. All that equals a little better efficiency.. Or so the theory goes. As well, with a cav plate setup (foot actuated) You can lower the plates quickly, run through some wakes, and then raise them quickly etc.. etc..


What is the function of the inner and outer cav plates on a set-up like the one above?

To be technical I'm pretty sure those are Tabs actually.. I'm pretty sure I've seen the inner ones both ways (Cav Plate style, and or Hinged style). (These are pretty short answers btw) The function of the inner plates is to push the bow of the boat down in the water when the water gets rough. In Ski Racing, you want to displace as much water as possible
when going through waves, to "lay down" the water for the skier behind you.

The outter Tabs, are used to cure chine walking. When the boat starts to rock back and forth they lower those monsters and the outter tips of them will dig in when the boat rocks.. Stabilizing the boat.


Why is the term "cavitation used to describe the plate system?

I'm going off memory here, but I think it had something to do with the guys name that invented them. Ironically enough Cav Plates cause less disturbance in the water then alternatives.


Do they cause cavitation at the transom? If so what do you gain from cavitation behind the boat?

See above.

Why do some mount trim tabs horizontally and others mount at the same angle as the bottom?

The ones that are mounted horizontally are more to help with chine walking, then providing transom lift. By mounting them this way, they can lower them and have the "tips" of the Tabs do all the work.. Less Tab in the water = less drag in the water. It also equals alot less lift though. Some people going for all out high end #'s will mount them this way as well. They still are functional as "tabs" (pushing the bow down) just not nearly the same amount of lift as a conventionally mounted tab.
conventionally mounted tabs, provide a decent amount of lift.. Helping a boat to plane at slower speeds, dig the bow down in rough water, etc.. etc..


How much movement up and down do the cav plates have? What is the advantage of the cav plates being mounted to the botton vs. hinged on the transom? [quote]

Cav plates typically don't move very far.. From what I've seen, anywhere from and Inch to an Inch and a half or there abouts.. The longer the plate, the less it'd have to move. A hinged plate would technically be a Tab. The setup I'm talking about building, is kind of a hybrid.. It's transom mounted, but flush with the bottom of the boat. The plates would bend like a cav plate, but not be routered in.

[quote]
Sorry for all the questions, I will be starting a new build soon maybe a Schiada 24 or 21 RC or a Hallett Vector or 210 laid up heavy for a smooth ride. I will be running a Bravo set-up with 600-700 HP.

You definately want to talk to Racey, or some other professional shops..


Where did you take 2' out of the 24 Schiada you are calling SR22? It's tough to tell from the photos? How does it do on a windy day at Mead through the narrows and across the Basin headed to Big Sandy Beach?

Thanks for your help?

From what I remember (don't quote me on it again) They shortened the boat 2' from the transom, by putting a filler block in the mold. It runs bitchen from what Racey was saying on Hotboat..

Incidentally, a side note here. A 22' Howard Offshore is a 24' Schiada that they shortened. You could basically order a SR 22, from Howard, and have Racey rig it. (This is providing, that Howard shortened the boat off the transom, which if memory serves.. they did)

RD <---- fingers are tired now.. :D

[Retired Member]

Chris I thought about doing the GT Style plates, but truth be told there a little much for what we're gonna be doing with this Spectra.. (I.E. 2 sets, inner and outer etc..)

To be quite honest as far as Tabs vs Cav Plates, I can't in the world imagine why anybody would want a tab over a Cav Plate? By Hinging it your having an abrupt change in water flow (more drag, less lift) then you are with a Cav Plate.. You can move the cav plate considerably less and get = or better results.. yada yada yada.. LOL

That and lets be honest here, making a cav plate is exponentially easier then making a bitchen Hinged setup. ;)

RD


He's saving that task for the GMT! ;)

[Flat Broke]

Dave,

Unless someone can give you a really good reason not to use the pillow block mounted setup, I think I'd go that route. I hear ya on the ease of machining a cav setup vs. tabs. I was just curious to know what you were looking to do.

When you get around to making some turnbuckle moutning pads, let me know because since we run the same hull, they'd be cut at the same angle, and as such I might be interested in picking up some for whenever I decide to finish my boat.

PM me your email addy, and I'll shoot you some pics of different pillow block mounted setups I have.

Talk to you later,
Chris

[RiverDave]

Send them to davej@johnsondes.com :) I always like seeing different setups!

RD

[Racey]

Where did you take 2' out of the 24 Schiada you are calling SR22? It's tough to tell from the photos? How does it do on a windy day at Mead through the narrows and across the Basin headed to Big Sandy Beach?

Thanks for your help?

Schiada built the boat model for one of our Arrowhead customers, It is quite a bit less than 2 feet taken out of the boat, the 24's are closer to 23 feet in length, but they took some entry hook out of the front to get away from bow steer, i believe it measures out to 22' 4", and the bottom was completely worked over by Brummett. The boat handles rough water, and chop phenomenally, it honestly makes a 21 feel obsolete. If it had a deck more like the 21 it'd be the hands down perfect boat in my opinion.

[scjohn]

Dave, Racey,

Thanks for your detailed answers. I wont be ski racing and will be happy if the boat tops out at 85, so I figure a good set of big tabs will be fine along with a straight bottom. The big tab/plate setups do look cool though.

Dave, Does your company do any work for the golf induudtry?

[River]

He's saving that task for the GMT! ;)

Gonna put another motor on there and hang with Reb? :D

[Retired Member]

Gonna put another motor on there and hang with Reb? :D

I'd have to put another 2' of freeboard also, just to float it.

[River]

Yep... :)

[River]

Here's another couple pics...