21 daytona bottom modifications

[Fonz69]

So I have a 21 Daytona that was built for an outboard and someone started a jet boat project with it and stopped after cutting the two holes. My question is I have seen posts where guys are saying the bottom Keel is designed more for a jet boat and not an outboard and is there any bottom modifications like cutting the center pod to make it raised and flatter from the transom forward a certain distance?

I seen a 19 daytona with flats on the rear with any outboard before is why I’m asking.

Ive been a jetboat guy but for this boat it might make more sense to go outboard being with a 300xs I could see 100mph without building a 1000hp bbc and sticking $10k in a pump and $4k in bottom work. Going to keep my plans on a 2 seater race jet boat separate and make this one a family river runner.

I can fill the cutouts from the jet drive myself as I have fiberglass experience and my father has been in auto body his whole career and can make sure it’s done right.

Has anyone tried this?

Hull weighs 1030lbs with twin 24 gallon tanks and besides that has never been rigged.

[Da Bull]

Seeing how the 21 was first a jet then adapted to outboard use there is plenty of mods to make it a better ob bottom. First is the transom with no tuck. This is normally done with a jack plate with some degree of tuck built into it.
Next is the bottom that was designed to keep the pump loaded. This is easy to see when looking at the center pod and how it tapers from wide to narrow. Then there`s the pad itself. No lift there. If I owned one of these boat`s I would make the pad wider and flat from side to side. Next I would add a lifting strake to both sides of the pod about an inch up from the pad thus creating more lift. After the bottom mods I would run no less than 15inches of set back and maybe more. However in looking at your pics and knowing the boat needs lots of setback why not cut a notch in the transom like all high performance ob hull`s have and use less setback. You have to repair the holes in the bottom and transom anyhow so why not.
Wally Lampkin at Triad Boats told me there is lots of speed to be found under these boats mainly because a jet boat is designed to suck down to keep the pump loaded and an ob need`s just the opposite.

Please post your results. There are lots of these 21ft Eliminators/Liberators/Cougars and such running around here.

DB

[F14]

Why modify it? Fill the holes and run it. Mine did 105 mph bone stock. If you want it to turn better I can see modifying it because its a drift machine.

[Fonz69]

F14

Thats what I’ve heard is around 100mph as is. I just figured if I’m fixing the bottom might as well modify it if it would help any. Just couldn’t find anyone who has done this yet. I did find pics of a 19 daytona that was modified.

Just St looking for ideas and options.

[Fonz69]

DA Bull

Not sure what you mean by notched transom? Sorry been a jet guy always. Do you mean cutting the bottom center pod up and forward like this was done to the sides on a 19?

[Da Bull]

Yes. That's exactly what I meant. Most all outboards have it. I have read where Howard Pipcorn invented that step but didn`t copy wright it. It just seems that you have to rebuild that part of the boat anyhow so may as well do it along with making the pad flat.

Also if you have no experience behind the wheel of a fast outboard please take it slow and learn. It`s way different from a jet.

F14, Making a boat go faster is what this website is all about. A long time ago my oldest daughter changed the color of her hair and I protested by saying in a very confused voice "Why did you do that? What was wrong with the stock color you came with"? Her reply was "DAD, Have you ever left anything stock"? I had no comeback to that.

DB

[Fonz69]

So I was debating about not putting the radius on the very bottom back in and going flat. Thoughts on this being good or bad? If good how far forward do I go with it?

[HavasuDreamin']

Eliminator made at least two bottoms for their 19' and 21'...or one bottom + inserts depending on the application. The jet pump boats always ran better with a rounded keel. It allowed the pump to load properly. The outboard boats had a flat keel. At a minimum, you obviously need to fill the jet cut outs and gel over for a smooth finish. The keel should be flat. If you want to go next step and put notches in the outer sponsons and center pod, that is up to you. It will run fine without the notches though. You will just need set back. On the inside, you should have knee braces glassed in from the transom to the stringers. I would also have a CNC machine cut precise aluminum brackets to further brace the inside where the external outboard bracket bolts through the transom. Those interior aluminum brackets should sit flush across the transom and extend to the knee braces and / or stringers.

[Fonz69]

So just had John Johnson owner of Recon boats at the shop yesterday looking at my hull. Plan is I am going to remove all the old transom down to the outside layer of glass, remove the damaged stringers ahead about 4’ and the balsa another 1’ forward of the hole in the bottom. John is then going to make a mold to replace the keel and we did talk about going flat however this is a heavier hull and yes the flat keel would help as a pad but he was concerned if at high speeds and turning the results of coming off that pad might cause handling concerns so for now we are going to return it to stock. The new transom will be 1/2” 3 ply layers. John also builds hulls for ski teams hanging 3 outboards off the back so I trust his knowledge on making a solid long lasting transom. As for the stringers we are doing the same 3 ply build and as it goes under the deck at the rear it will raise up and bond to the transom and top deck all in one clean piece, much better than the current 2 piece 2x8 and extra section glassed to it.

After all that work is done the next plan is to tape off the current colors and match it to my 69 Corvette color that my dad and I custom mixed we will have a 3 or 4 color fade to a gold pinstripe around the outside of the stripes that gold color is actually one of the layers of the candy color. It should look great when it is all complete I will try to keep up with posting pictures as the progress continues.

I am right now looking for the best transom bracket set up for a 21 daytona the plan is running a mercury 300xs and from what I have read anywhere from 12 to 16 inches total setback anyone have any pictures or 21 Daytona that is running great please let me know how you’re setback is rigged. Was thinking using a Bobs machine jack plate also.

[Fonz69]

Here’s a pic of my vette that the colors will be matched to.

[Fonz69]

Eliminator made at least two bottoms for their 19' and 21'...or one bottom + inserts depending on the application. The jet pump boats always ran better with a rounded keel. It allowed the pump to load properly. The outboard boats had a flat keel. At a minimum, you obviously need to fill the jet cut outs and gel over for a smooth finish. The keel should be flat. If you want to go next step and put notches in the outer sponsons and center pod, that is up to you. It will run fine without the notches though. You will just need set back. On the inside, you should have knee braces glassed in from the transom to the stringers. I would also have a CNC machine cut precise aluminum brackets to further brace the inside where the external outboard bracket bolts through the transom. Those interior aluminum brackets should sit flush across the transom and extend to the knee braces and / or stringers.

As far as I have ever heard of Greg Shoemaker explained that the 19 Daytona was first built with the flat keel then the bottom was changed to a round keel for better jet boat use. The 21 never had a flat keel but maybe inserts were used by a group like DCB possibly. I’ve never seen a 21 with a flat keel but would be interested to see anyone that ever tried it.

I also took measurements yesterday regarding the side sponsons to center pod and the center pod tips down by 1 degree toward the transom.

My concern modifying the center to a flat pad is in its original design with a radius it seems to get boats just over 100mph where as making it flat would show what kind of gains?

[Fonz69]

I also like this setup on a newer Daytona and am planning on making braces like HavasuDreamin was describing.

[Fonz69]

Don’t remember where I found this pic but here’s a good look at what my bottom of the hull looks like.

[HavasuDreamin']

Yeah, those are the types of aluminum brackets I am talking about. I would either call Eliminator, or otherwise check to see what type of bracket the west coast guys are using. Not sure if they are buying their stuff from RexMarine, Eddie Marine, CP Performance, some other outfit, or making them in house. My guess is you are going to need 12"-14" set back. Good luck on the rounded keel. My 19' had a flat keel and was a fairly heavy boat, albeit not as heavy as your 21'. My 19' handled excellent with the flat keel. Keep us posted.

[JPEROG]

If you want to be safe and not guess then I would take a look at the 21 liberator keel and do something close to it. It is not flat but has a very small keel in the center with negative angles to the outside of it. If you want to gamble like I would, take a close look at an STV pad and go that route. I would make a call to Wally and or Jack and get their advice first but my guess is going that way is where its at.

Joe