22.2 questions

[jsink]

I have a yamaha Vmax 200 with a 20 inch shaft and was looking at redoing a 22.2.  I'm looking at both the flatback and 12d hulls, but right now I'm leaning toward the 12d hull (unless the right flatback deal comes along ).  I've read through alot of the old posts and found a few discussions about the 222 flatbacks (pre-72) regarding the recommended motors and speeds, but I didin't find any info on the 12d hulls (post 73) regarding hp and speed.  My questions are as follows.

1.  With a porta-bracket or jack plate, will the 20 inch shaft work alrighton a 22.2 with 12d deadrise?
2.  What kind of performance should I expect on the 12 d model. I saw where top end on the flatback is 38-40, but the 12d model has lifting strakes.  Does that help any or is this still a "plowing" hull?
3.  Has anybody ever tried adding a "pad" to a 12 d boat during a rebuild?  An 8-12 inch wide pad would knock off 1-2" of draft and would 'in theory' provide a performance enhancement to the hull with the right prop.  Just curious if anyone has tried it or knows why it would or would not be a good idea?
4.  I have yet to see any info on the gas tanks on these boats other than seeing that most people move them forward when adding a bracket.  Based on the rebuild pics I've seen, there doesn't appear to be enough room below deck for a below deck tank - what do most people do with the tank?  Under the CC?  Have custom tanks made for under the floor applicaations?

Thanks,
         Jeff

[Radioshop]

The 12d hull and, the flatback both will plane.  The only time you'll resort to plowing is when the seas cause pounding at planing speeds.  I can't imagine putting in a pad would be easy or cause that much of a benefit to justify the effort.  The flatbacks do not have below deck fuel tanks, 12d's do.  Because of the narrow beam, you want to be conservative when it comes to adding transom weight.

[captflatback]

I have a 68 flatback and my tank is under the deck and i think it's around 65 gallons i hold. I had it custom made by Marine Specialties in Olsmar Fl here is a linkhttp://www.marinespecialties.com.

Capt. Jim Lemke
www.lighttackleadventures .com
813-917-4989

[Rayos]

Custom made for under deck.  Once the floor is out you will need to re-arrange the stringers by adding a bulkhead compartment to accomodate the tank then fit it in ( basically a rectangle).  From that space you order it custom.  Mine is a '71 flat and the tank is 53 gallons.  I use the space in the console for batteries, stereo, fresh water pump, elect panel..

[jsink]

Thanks for the responses, I figured you guys were having custom tanks installed.

Still curious about the performance numbers - haven't found any on the 12d hulls - only flatback numbers which seem to top out at 41 mph with a cruise of just over 30 mph.

As for the pad, I was just curious. If you strip the entire hull down and clean out the waterlogged foam from the stringers, adding a little pad back there would not be that much bigger of an undertaking. I know this isn't a performance hull, but it would decrease the draft and running depth by a few inches - possibly more. If you could use a porta bracket and trim tabs and the right motor/prop - you might be able to break the hull "free" from the water drag and really pick up some top end speed on calm days.  Just curious, but it looks like nobody else has gone that route.

Thanks again.

[Radioshop]

My lack of knowledge about putting in pads may show here, but in order to put one in, I would think you would need to change the geometry of the hull's deadrise in the area of the pad.  If you didn't, wouldn't you end up with the front of the pad being lower than the back edge of it?  Does that make sense?  In other words, wouldn't you be creating a mild reverse flat bow at the transom?  Maybe rather than a pad you should look at doing a tunnel?

[jsink]

Thanks Radioshop,
You are correct that it would be changing the geometry slightly and anytime you do that you may affect performance whether good or bad.  A pad is MUCH easier to add than a tunnel.  Basically, if you flipped the hull over and looked at the transom, your pad would look like a symetric triangle around the keel.  Let's say it was a 12 inch pad, you would go out 6 inches on either side of the keel and then draw two angled lines back at the keel starting at those two points. You would vary the angle of those two lines to adjust the flatness of the pad.  IN THEORY, if you ran your boat outfitted with all of your gear and then adjusted the trim tabs, jack plate, and trim just right your boat would be riding with the bow up at some angle. If you set the pad so that the leading edge was just slightly higher thant the trailing edge with the boat trimmed out properly, the pad would act as a center trim tab and help raise the boat up out of the water a little more and minimize drag.  This lets you plane in skinnier water and because of the reduced drag at the outer edges of the hull, will also increase you top end speed substantially. This can be done to any hull, but the problem is getting the angle right. Too little angle on the pad and it does nothing, too much and it causes too much drag and buries the nose. Just changing the prop will throw everything out of whack. Just curious if anyone had tried it since one of the benefits of this hull is that it will run shallow - with a proper pad, the 12d hull would run in shallower water than the flatback.

As for tunnels, they can be a nightmare.  The tunnel has to be designed to actually 'suck water' up into it.  Any shape will get water there, but if it isn't designed right, the turbulent water flow will leave the engine prone to water blowouts and "sneezing". Also, in order for the tunnel to work properly, most boats must ride flatter rather than bow high like a performance boat which will actually slow you down even further because of the increased drag.  A properly designed pad boat will actually run in just as skinny of water at high speeds (like bass boats), but when you come off plane you sit deeper and you need more water to take off.  I personally think a tunnel on a flatback would be phenominal, but a 12d hull would be much better served by a pad. I just don't know if I want to be the guinea pig!  

[RickK]

You lost me.  I can't imagine what it would look like. Is this something that is added on the bottom of the hull forward of the transom?  Is there a site that I can go to that would show what "pads" are?

[jsink]

http://www.fish.state.pa.us/Fish/angler ... athull.pdf

http://en.wikipedia.org/wiki/Padded_V-hull

http://www.hydrostream.org/ArticleArchives/HullTech.htm

Never found a good picture, but here are some links that give you a better description.

[RickK]

Thanks jsink.  They're all helpful.
The last link really is very interesting (to me anyway) and the top pic shows a pretty good shot of a pad when you click on it.  The hulls they are talking about are sick - 100+mph with a 240    Seems they don't take advantage of the pad until over 60mph - guess that leaves me out.  

[Radioshop]

Sounds like alot of effort for a relatively small benefit, but hey, if you're motivated, go for it!