how to set up a 30' cat with single drive?

[502procharger]

Anyone out there have any ideas on what would be the best way to set up a single drive hung off the center pod of a 30' Chris cat? I have seen many 28' singles but never any 30' how do I determine how much lower my prop shaft should be below the bottom of the side sponsons? Anyone who can be of any help I would love to here from. All ideas welcome.

[DogHouse]

The center pod on that hull is way above the outer sponsons right? If so you should be able to mount the propshaft at the same depth as the outer sponsons and the prop should get enough clean water to get on plane. I had a 20' pure tunnel (no pod) that was setup that way and it did ok coming on plane. With the big boat, single drive, and high X dimension, I think you might end up needing a fairly large prop (16"-17"). In any case I bet you end up doing a lot of prop testing before finding the right one. Are you using a speedmaster drive or something else? Unfortunately I think it's all a bit of a guessing game since you're in uncharted territory, and it's not exactly easy or cheap to change the drive mounting height once you've cut the hole! I suppose if you're in doubt it's better to go deeper and make sure the boat will plane. All you sacrifice then is some top speed. Good luck and post some photos of the transom/drive if you get a chance!
-brian
[ December 11, 2002, 03:27 PM: Message edited by: DogHouse ]

[502procharger]

Thank you for the input Brian. I was planning on going like 1" 0r 2" below the bottom of the side sponsons. What I would like to do is run like a #4 drive because then at least I can add or remove spacers to drop it or bring it up. Any benefit to running a stand off box in a situation like mine? I had thought that maybe if I get the drive out from the back of the boat a bit I might get some better water to hook up in. any input would be great. I have no problem sacrificing a little top end for some satiability. I do not want it to rock back and forth sponson to sponson.

[HeavyHitter]

I wouldn't set the #4 any further back than it is bolted to the transom. I have a #4 on a 23' tunnel and added an extension box to fit the transmission without loosing interior space. It's plenty long. Trimmed up it to trailer ends up 54" from the transom to the skeg. The boat porpoises more than I'd like at low speed. Once you get it around 50 it's smooth sailing. Props are hard to come by for the older small shaft drives (2,3,and 4). Most have been bored and resplined to the later model 3A, 5, and 6 drives. Be prepared for sticker shock, new props are start at $2700. My boat has the prop centerline 2" below the center pod which is the same depth as the outer pods. It is lazy out of the hole. Just as the boat starts to nose over the prop breaks loose till the boat picks up a bit of speed and planes away. Good luck.
Wally

[502procharger]

come on guys, i dont want to start cutting holes in my transome without getting some more info.

[DogHouse]

Can you post a pic of the transom that clearly shows the center section in relation to the outer sponsons? That might help. If I'm not mistaken your boat is very similar to the 31 AO correct?
-brian

[502procharger]

i will soon, i think it is the same hull.

[502procharger]

http://free.***boat.net/gallery/Forum_Graphic_Depot/DSC03247.JPG
http://free.***boat.net/gallery/Forum_Graphic_Depot/DSC03248.JPG
http://free.***boat.net/gallery/Forum_Graphic_Depot/DSC03289.JPG
disregard the outboard mounts and stand off box
[ December 12, 2002, 08:49 PM: Message edited by: 502procharger ]

[DogHouse]

Thanks for the pics, interesting stuff! The last shot that really shows the bottom is a little dark on my computer, but it looks like the tunnels are very deep and the center v-pod is wide and shallow, giving you a lot of depth below the pod to the bottom of the sponsons. (maybe 12" or so?) I personally wouldn't put the propshaft any deeper than the bottom of those sponsons. There should be plenty of clean water on the top half of the prop to get decent bite at low speed before the boat comes cleanly on plane and starts to lift. If you're trying to go fast then you really want as little of the gearcase in the water as possible when the boat is aired out. I bet you could even run it up a couple of inches and still get away with it. If the center pod was full depth then it would be a very different story. Only problem I'm wondering about is how the heck you're going to get a #4/5 SSM mounted low enough to get the prop anywhere near the water. Those things are really short, something like 5"-6" shorter than a #3/3A if I'm not mistaken. You might have to go with the longer drive in your application, or a #6 if you feel like spending some real dough! Have you talked to any of the industry experts to get their opinions on this setup? A quick phone call to someone who has set up a lot of different boats (Teague comes to mind) might be a good idea. Good luck!
-brian

[502procharger]

a #3 is 5 inches longer but you can put up to 6" in spacers in a #4. I really need to get some measurements on the #3, #3a, And #4 without spacer. it is like at least 12" from the bottom of the centerpod to the bottom of side sponsons. I still have not bought a drive and i will continue to search for people who have good info for me before i do anything. i thank you for the help. if you think of anything that might help me or have any contacts please send them on to me.

[502procharger]

anyone know how far a #3A drive propshaft hangs down from the bottom of the gimble?

[nhbuoy]

HEY 502PROCHARGER...Why dick around with the MERC stuff(ESP antique drives)???In your particular application I would be thinking KAAMA or ARNESON drives...Pretty much ZERO drag(ESP since you will be driving off the CENTER POD of that particular hull),completely trimmable,they are INDESTRUCTABLE,LOW maintenance,& BIG horsepower w/reliability is NOT an issue...There are other advantages as well but I don't want to overstate the case...Let me know if this is an option...

[502procharger]

my problem is getting the prop into the water with a surface drive and such a shallow center pod. take a look at the picture a few responses up and you will see what i mean. i need something to hang down to about the same hight as the bottom of my outside sponsons. any ideas i would love to hear them. :)

[DogHouse]

How about a V-drive? Can the thrust angle on them be altered? On a big boat like that you could mount a V-drive way forward and use a long prop shaft to reduce the thrust angle. I assume you'll be using some sort of transmission with that turbine. Interesting project ya got going there!

[502procharger]

i am open to any ideas, i have the boat and the turbine. drive system as not yet been worked out. i really do not mean to sound stupid b/c i have no v-drive experiance but what is thrust angle? and can a v-drive be used on such a big cat. If so how do i determine where the prop shaft must end to work with my hull? again anyone who has any info or ideas for me please help. I was planning on mounting both the turbine and a v drive gearbox on the same angle so that the output of the v drive gearbox ran parallel with the bottom of the center pod so i could connect a driveshaft between the output of the v-drive and my trans. then out to whatever drive i choose. i could also skip the trans and go to a b-max, but i do not think it would hold up. HELP!!

[nhbuoy]

HEY 502PROCHARGER...OK, I didn't look at your pix close enough, BUT, I think those KAAMA/ARNESON drive(s) MAY still work...They are a TRUE surfacing unit & with alot of length off the center pod I think the water "break" will be high enough that it probably won't be a problem...Call Howard Arneson...He has a SKATER (NO C-POD!!) with a turbine & one of his drives(at least I THINK it's a single)...BTW...Those drives are chain driven so synchronizing two of them off one power source isn't a big deal either...Let me know what you think....LATAPOTATA>>>>>>>>>