Slippery Botttom

Yes, a layer of air bubbles...

Or better yet keep the hull out of the water on hydro-planes...

John.

electroman:

The new hullsl do just as you said--"air", However their built into the hull mold--little difficult to modify my hull-I can only push the hp up and do some minor hull mods--I still believe there is a material that can be applied to make the hull "slippery"--Maybe someone will see this thread and know the answer? We'll see.

Thanks for your thoughts--Donzi.

Hey Electroman:

Your panda's having a fit--Better call the doc.

Donzi

Yes, AIR, is the best you can go, I remember a surface they called "Shark skin" or something like that? It resembeled a orange peel surface, all rough to the touch, Far from slippery you would think to be the best. But, it caused a million tiny air bubbles to become trapped between the surface and the water, reduceing the drag by a large amount.

I used to use VC17, which is made in several formulations, most or all containing teflon.

Blink:

what is this vc17? never heard of it--is it a paint/wax/?

where would i get such an animal?

thanks--donzi

VC 17 is a bottom paint. The stuff I used to use came with copper powder that you added as you mixed it up. You could roll it on and get a smooth finish. It can also be sprayed with an airless sprayer, but not a standard sprayer -- it dries in mid air.

may be military pseudo secret --

inject "polyox" -- soluble polyethylene oxide (in solution) -- onto fore hull

huge delta in friction coefficient

(has been "illegal" in drag racing circles in the past)

good luck & be careful -- your donzi will eat you given a chance with chine walk at speed

guest

what is this "polyox"--a paint /wax/?--will it stay on the hull like paint?

Appreciate the chine walk advice but you obviously haven't driven a donzi--they don't chine walk at any speed and mine ( "87" Z 22) , being pushed by a 570hp big block runs into the 80s (like driving a big car down the interstate on sunday) and it doesn't matter how rough the water gets (likes 1 foot chop)--After i built the engine it was supposed to run well in the 90s but 80s is all i can get--being a 87 hull there are no provisions for "air", as in the newer hulls, so i'm thinkin, "treat the bottom with slippery paint (whatever) and maybe add chine's close to the center beam to simulate a "pad" which is what all the newer fishing boats are using for speed ,athough they're dangerous if you don't know what you're doing.

thanks--donzi

HughMattos:

To clarify the donzi==It's an "87" Z22 with an 570hp merc BB with out drive running a 23 pitch wheel into the 80s. By calculations, it should be running in the 90s but several factors restrict top speed (lack of "air" design in the older hull, lack of chines to simulate a "pad" at higher speeds and the wide beam donzi uses in their hulls for safety and ride). The boat is heavy which is a plus except for speed--

You're the second reply that has referred to the "shark skin" finish and possibly a strake add to both sides, just above the keel area (to simulate a "pad") to reduce surface area at speed . At this point i'm thinking the bottom finish (type) and the strake add (to simulate a "pad") might be my best bet.

PS--This hull doesn't like "calm" waters--Loves 1' "chop".

Thanks for the info--Donzi

Donzi,

I would be a bit concerned to see you running a 23 inch pitch prop at that sort of speed - what gear ratios are you running and what is your engine revs at max power?

We are generally outboard boat builders, but we see max revs on an Evinrude 225 at 65 - 70 mph with a 23 inch pitch 4 blade stainless prop, so I would expect you to need a much bigger pitch to see 90 mph

Good Luck

HughMattos:

Know what you're gettin to--mathmatically doesn't seem right--Engine only turning 4500Rs--stern drive is 1.5 ratio-wheel is surface piercing ( i call it meat cleaver)--can't get it to slip if you wanted to.

Engine was built Merc 468ci (570hp) to turn over 6k but can't get it over 4500 (either have s blown power valve in the carb or the engine can't overcome the hull drag) though not much is in the water at 80.

Larger pitch wheels are a problem , with a load and boat weight, it's hard to get on plane because the holly carb want's to load up and shut down the engine (no prop slip) before you can obtain plane speed.

After i've reviewed my hull options, I plan on sending the carb to special shop to have it analized for trouble and jetting.

Appreciate the info--Donzi

If the hull is clean and smooth, maybe your engine is not putting out the advertised HP. 300 - 330 is pretty typical for 454s in marine use. I used to do dyno testing of "100 hp" motorcycle engines that only put out 50-60hp. If the prop is sized for 570 hp and you can't get the engine to its HP peak, then the engine is not really putting out 570 hp. Have you tried less pitch?

Blink

You're right it's a merc 468ci-570hp but the problems not with the physical makeup of the engine, it's probably the carb or ign cause it won't turn over 4500 Rs--I know I've got to locate the rpm problem but I'm looking for ideas to reduce the wetted area of the hull or or install a "slippery" surface (which doesn't look real promising to date) until such time as I can find time to attack the rpm problem.

Doesn't matter which pitch wheel I use, the rpms just won't come up.

Thanks for the info--PS see you finally got some rain--That's got to be a relief.

Donzi

there is a company called Maxiglide in the U.S. that has been supplying Olympic kayakers, canoeists and sailors for years for this purpose. plus most of the major college rowers use their product called BoatGuard SPF-50, a teflon based polish, extremely hydrophobic and anti-static that repels water and surface tension which is then replaced by air to give the hull minimum resistance thur the water thereby increasing speeds up to 5% based on hull design. it generally is used on smaller craft as it needs to be re-applied every couple of months. I understand that they do have a more permanent coating for speed enhancement that also includes a natural, non-toxic anti-fouling component.
see www.maxigilde.com.

guest

I'll look into this --don't want to re-apply every few--but i'll look into this more permanent coating you've directed me to---

thanks--donzi

Donzi, I sell coatings for the Marine industry and you are more than welcome to call or email me regarding Marine Hull coatings. As per your question regarding Teflon, Teflon when put on hull actually slows the ships/boats down and depending on the coatings absorbs water into the coating. We have tried many additives and the best one that has worked so far is our SP 1386 SA. This product is a 100% solids coating and has a silicone slip additive added into the formulation. This product is used anywhere you need a slippery surface. It makes the surface become hydrophobic in nature as well, due to the solid content makes the surface very smooth. This coatings is used throughout the Canadian Navy, Canadian and US Coast Guard as well as 100's of commercial ships and barges. We have never put it on a Donzi boat, but I am confident it will work.

Feel free to call at 778-2316027 if you would like more information.

marine boy:

Are these coatings available in color (yellow)?

My hull is almost like new for a 20yr hull and I really don't want to change the color. Do you feel the coating you refer to will actually increase top end?

Thanks--Donzi

Less a big block, your older Donzi is kinda limited, in it's current stock configuration.

Teflon won't do anything provable, (but seagull eggs won't stick to the boat hull). LOL

Unless you go Hydro-foil, your not going to have much luck with adjusting H20 surface tension with a coating, in my opinion, that is unless you can find a way to scare the molecules out of your way, before they hit the hull. (Or fly over them, as discussed).

Weight reduction is your best route. Start drilling out every other support with a hole saw and removing everything you don't absolutely need to hold the boat together. Redesign the structure lighter than what Donzi gave you. They didn't start using CAD until the mid 80's, so some of the older hulls are much thicker than they need be. (Not sure of your particular hull, as you didn't offer those details).

Carbon Fiber hull supports will work well.

Here's the latest design out of composites, to get you in the mode:

[link]http://www.earthrace.net/index.php?section=3[/link]

These guys ^^ are going to go through the waves, instead of over them. Straight line theory.

If you want to do some R&D and use lighter engines, with higher HP, check out these guys:

www.mazworx.com

They are going to get well over 600 hp from a turbo charged 2.0 stroker, Nissan block 4 cylinder. Last year Maz broke 9.42 in the quarter mile with a 4 cylinder SR20 block. In fact they claim they can get 1100 hp, with major mods, this season.

600hp, from a detuned engine like he can build for your boat, should be darn right reliable, on an engine "engineered" to spin much faster, and be cooled in the water. The custom water manifold will be a few bucks, but you'll easily sell a few, if it works out OK.

Lighter, faster, stronger. I'll bet you drop over 150 lbs. of engine block and increase your weight to power ratio exponentially, using aluminum sleeved / Teflon water jacket coated 4 cylinder engines. Ask Dupont if they can coat your engine block water jackets, so they don't corrode from brackish water, instead of your hull. Might last a bit longer or improve efficiency with cooling system flow, just from lack of slag and corrosion build up.

I have been considering what a drag boat with such an in-board power plant will do on water, using methanol injection. Mazworx engines can spin over 8500 rpm. That should get the turbine or aft shaft moving.

Do you have room up front for a 4 cylinder engine? Cut the hull for intake and tilt a 4 banger and turbine Jet-housing to the floor.

Lose the aft-shaft and relocate the transmission weight forward. You'll have a great new design, with reliable power, at half the weight and better emissions, because of the turbo charger / methanol injection and an AEM engine management system, under turbine drive.

Weight reduction, reliable increased HP, at proper trim and turbine drive propulsion systems, are your solution to speed, on an older hull.

If that's too much work, build an old 1980's 15' Hydrostream, instead. The Merc 325 hp X-Outboards are the fastest, cheapest way to make a potato chip run fast, unless you want to re-invent the wheel. (The turbine wheel).

By the way, Merc builds and tests the 325's, right near Mazworx, at lake -x in Orlando.

Coincidence Hmmm...

Moto:

Too late to discuss lighter engines--Got $12k plus in this 570hp big block which has had all heavy iron parts replaced with alum w\e of the heads (couldn't afford them at the time) in an attempt to lighten the already heavy "87" donzi Z22. (It's built like a sherman tank)--rides like a caddy . The hull, like most donzis' is wider, for a stable ride, and being a deep vee has great handling capabilities in almost all water conditions . Being a "87" the "air" technology was not around so i'm sorta stuck with minor hull changes such as coatings and chine modifications/adds.

I wouldn't change the boat physically other than minor things cause it's still worth big bucks in it's original condition.

You have some great ideas--and i thank you for the info.

Donzi

What about the west syetem epoxy with graphite powder mixed inmto the mixture. I have seen many sail boats with this on its bottom and I hear it works well in open seas for speed. I know it mixes well because I have made it up on several friction points that were expected to rub a bottom and drag on a smooth surface and ware like steel. Look into it!

D. J. Borek in Austin, TX

A few years ago, I purchased a product called "SCATT". From Their web site:

http://www.boatersland.com/scatt.html

SCATT is a dry film coating which aids performance and minimizes or eliminates fouling. Makes all boats go faster. SCATT keeps hulls cleaner and efficient, reducing drag tremendously. Boats get up on plane quicker. No ugly bottom paint. Reduces fuel consumption; less drag = less fuel consumed. Top speed is faster.

I used it, and saw a slight increase in top end.

MechanicOfNY:

Ill look into this stuff--looks intresting!

Thanks--Donzi

I've seen the Donzi; it is a really pretty boat, and I can imagine it should be quite fast. I understand wanting tomake it faster. Just remember there are limits to what can realistically be done.

The coatings discussed here are not used to reduce drag, but rather to eliminate potential causes of increased drag. The polyox has properties that prevent certain types of biologic growth on the hull. Th SPF-50 is a hull polish. The Teflon particles make it penetrate better and last longer. Beyond keeping the surface more smooth, no polish will reduce drag. (The Navy has looked at everything possible in this regard and there is nothing out there more than an urban legend.)

Most technologies used to reduce drag do so by reducing total wetted surface to eliminate part of the surface resistance. Eliminate equipment to reduce weight, vessel rides higher and wetted surface is reduced. Lift the hull out of the water, reduce wetted surface and resistance tends to go away. A surprisingly good quick discussion of most of these technolgies is available at Bently Yachts web site http://www.yachtboutique.com/BentleyYachts/Advanced_Hulls.htm

You might look at the "Blade Runner"approach. VERY counterintuitive approach. Navy developed this technology at their Carderock Division in Maryland. It amounts to a shallow dam under the stern (second one amidships is not useful on a smaller vessel.) Seems like it would put on the "brakes" but it doesn't. It does strange things to the pressure profile under the hull, and seems to create a static water interface over which the passing water runs, so that the the resistance is based in water-water contact rather than water-hull. Very strange! But the Navy is convinced it works (went so far as to patent it - look it up - and uses it on numerous vessels from high speed SOF boats to destroyers.) and so is Bentley. There are public domain research reports, too. (It was tested here at CD.) You might give it some thought.

(I don't know how tall it should be, but maybe 2 - 2.5 inches (50 - 60 mm.))

That, and tune up the power train. Best I can offer. Hope it helps.

Sam

Not that I know of. At power boat speeds the coatings all wear through in fairly short order.

Pretendgineer:

There's a lot of opinions on this technique, most questionable, some outright negative.

Getting the hull "out" (less wetted surface) will probably be my fix in the end.

Thanks for the info--Donzi

Good luck achieving your goal. I've got a 58MPH Baja 252 so I'm not in the area to be too concerned by friction. Others in the forums I use (with the quest for speed) will check for a hook in the hull by the transom. Also blueprint the hull.

On a separate note. A friend with a 1970's 28' Cigarette w/ twin 650HP 502 blocks cannot break 80 in smooth water. Once a small chop kick up it'll break free and the boat will rocket into the low 90's.

Pretendgineer:

Mine does exactly what your friends Cigarette does--Hates smooth water--Needs to have chop and you're gone.

Thanks--Donzi.

PS--Afraid "hook" will pull the nose down or disable trimming the hull "out" at speed.

Donzi,

Seems likely that tuning up the engine would result in the push that is needed to plane properly. If it is confirmed the engine is already tuned and running properly, shaft bearings are good and the hull is not damaged, it leaves the screw. If you get to that point and there remains a problem (and you think it might be helpful) contact me with full description of the screw and its deployment. I will see if one of our experts won't talke a look at it.

Good luck to you, and enjoy!

r/

Sam

Visor:

As I explained to one other-the carb is questionble, at least in my mind, a new holly 900cfm marine-think I may have blown one of the power valves-got an outfit in Atlanta whose going to look at for that problem and the jetting for me--the rest of the engine is fine I,m sure (only 30hrs)--The screw has never been a problem before this condition showed up. Just can't turn up the RPMs.

The hull area I,m looking at is just experiment to see if additional speed can be obtained with hull coatings (doesn't look good at this point) or hull mods (strakes/pads,etc.) --we'll see.

Appreciate the info and the offer--May be talkin to you again.

Donzi

Try www.mclube.com. They have a coating called sailkote. I don't think it is for the bottom of hulls, but you could try.

Plas-Tech:

Have already left an inquiry with this company.

Thanks for the info--Donzi

Having just come across your dilema I offer some thoughts.

Have you confirmed the ignition timing for the fuel that you are using?

Has the engine been ported? (Are the ports of the block and the manifold smooth and matching?)

Are you using the best lubricants for speed?

Do you have a torque / horsepower curve for your engine?

Have you had the engine tested for torque and horsepower rating?

Does it match the prop that you are using?

It may be that the prop is overloading the engine. A good propellor shop should be able to confirm the prop pitch and diameter. You will need the prop clearance radius.

Sailboats tend to go faster when the hull is lightly sanded in the direction of water flow.

Speed - there's (almost) nothing like it.

popfar

Ign. timing is standard for merc BB but the manual timing (cam) has been retarded 2-3* in an attempt to recover some HP at higher RPMs--

Yes the engine is ported and all ports were matched--engine has been completly blueprinted (100s of hours and 12k worth of goodies).

Since I don't have access to a dyno, I have built the engine using high performance computer software programs where you can vary infinite parameters to insure maximum effect.

Could be the 23 / is a tad high for the wheel since i've always used 21 (meat clevers in the past) but the HP should be able to handle this pitch.

Since I selected a high duration cam 238* @ .050 (292 advertised) I also elected to use Rhodes variable duration lifters in an attempt to regain my low end torque to get this beast on plane.

As I noted in prior discussions-I had no problems the first several launches--this problem (not being able to pass 4500 RPM) just popped up recently and I suspect the carb (850 DP Holley) which I am currently having evaluated by a carb shop in Atlanta.

After studing the many suggestions so kindly offered I believe (after carb analysis) that I will install a short strake (both sides of course) just outside the center beam and hopefully in the proper location (bow to stern) to create a "pad" to lift the hull and reduce the wetted surface at speed.

I'm a little reluctant to treat the hull with material that gives it a "shark skin" finish (although it sounds like it could be a positive move) but why haven't the competition boats gone to this finish?

Appreciate your input-and you'r right "speed there's (almost) nothing like it"!

Donzi

You seemed to have covered all of the issues.

I seem to have missed the "just popped up recently".

What happened recently? Something fail, change?

Carb could be the issue as could be fuel pump and filters.

How is your fuel pressure and volume at pressure? (Fuel pump OK?)

Good call. The E10 ethanol "fuel tank cleanser" carries all kinds of gunk into the sensitive carb jets and filters. The jet opening which is the size of a pin and fed through a low pressure differential, can be easily obstructed. Inadequate fuel supply means running lean, which pushes the danger of burning valves.

Popfar

Had a couple of backfires --suspected the fuel valves but the carb is supposed to have blowout protection.

When I get carb back , I'll check fuel pressure /volume--I'll guage everything when I take it for it's test run--soon I hope. If it continues to crap out at 4500 rpm and all the fuel readings are within limits , I'll just have to start with prop changes, engine diagnostics, until I find the problem.

Can't be that difficult.

Donzi