Prather 40" Mono Setup

[Propjockey]

I have a Prather hull that originally had an OB hung off the transom and now would like to make it an inboard. Any setup pointers? I'm not sure if a hull this old can run efficiently with a surface drive.

I know there's a kajillion of these hulls out there...anyone remember how theirs was setup?

 

[crrcboatz]

That hull was intended to be sub surface. If you set it up surface be careful not to over power the hull. It has a lifting bottom ie the strake configuration.

Curt

 

[oldlugs]

Agreed; sub-surface was what they're intended for, and they work very well that way. If you're needing any set up specs for it, I can probably still find my original booklet for the Prather 40"... I built one of the early style (called the "classic" when the newer style deck came out) about 17 years ago. BTW- I recommend that you use better hardware than Prather's (like Speedmaster or similar), and a modern radio box.

Duane

 

[dannyual767]

Sorry to hijack your thread Propjockey but I've got to ask these guys a similar question. I've got an old Dumas DV20 that I've rebuilt and shot with PPG urethane primer. It'll get color this week . Anyway, it was a subsurface drive and now I've converted it over to surface. The hull has strakes and I'm powering it with my brand new OS 21 RG-X with an Irwin quiet pipe. Its just a sport boat. Am I going to have problems with the strakes/surface drive?

 

[Joe Warren]

Sorry to hijack your thread Propjockey but I've got to ask these guys a similar question. I've got an old Dumas DV20 that I've rebuilt and shot with PPG urethane primer. It'll get color this week . Anyway, it was a subsurface drive and now I've converted it over to surface. The hull has strakes and I'm powering it with my brand new OS 21 RG-X with an Irwin quiet pipe. Its just a sport boat. Am I going to have problems with the strakes/surface drive?

PropJockey, the older sub surface drive boats had breaking point 3-4 inches in front of the CG. These boats had a longer wetting surface, They require the lift the subsurface provides, Converting them to surface drive will not allow the Hull to lift. Put a straight edge on the bottom of your mono hull about 1/4 off the keel line. Measure forward towards the front of the boat Until the bottom No longer is Flat & it begans to swep towards the front Nose. (This is the breaking point) If it is far farward of the CG? 4-5 inches) the hull will work best subsurface, Now if you want to know about where your Cg is?? It is almost exactly in line with the front of your flywheel.. The Modern Surface drive boat hulls(Non Hook type Boat Hulls) the Breaking point is about 2 inches in front of the CG. They work great because of the shorter riding surface. They all Pivot or turn @ the breaking point.That means they must wet the hull up that far to turn..... Good Luck! Hope this helps

 

[Propjockey]

Thanks for the info guys.

Where should the balance point be? There's no engine mounted yet (or rails for that matter), so I don't know where the flywheel should be. A straight edge along the keel shows the breaking point about 17 in. from the transom...way forward I'm thinking.

Oldlugs...the original setup booklet would be kickin. If you can lay your hands on it, I'd love to get the info. And I have some older Marine Specialties hardware I was planning on using.

As for overpowering the hull...I'm leaning toward using a .60 aircraft engine with a machined "wet head". I know the port timing is less than optimal, but it's super reliable and easy to tune.

 

[oldlugs]

Thanks for the info guys.
Where should the balance point be? There's no engine mounted yet (or rails for that matter), so I don't know where the flywheel should be. A straight edge along the keel shows the breaking point about 17 in. from the transom...way forward I'm thinking.

Oldlugs...the original setup booklet would be kickin. If you can lay your hands on it, I'd love to get the info. And I have some older Marine Specialties hardware I was planning on using.

As for overpowering the hull...I'm leaning toward using a .60 aircraft engine with a machined "wet head". I know the port timing is less than optimal, but it's super reliable and easy to tune.

OK then; I just dug out the Prather 40 inboard mono booklet for the older version hull (original deck, but the same bottom as current ones, I think). Prather says to center the glow plug at 13" from the transom. They say the CG should be around 12" from the transom.

On mine, I centered the plug at 13-1/4" from the transom, and it still ran pretty loose 'till I dialed in a little negative prop angle to keep the nose down. CG on mine is about 12-1/2" from transom, from memory. I suspect that mine was built a little lighter than one using all Prather's hardware, and it runs a massaged Picco .45, and last ran 50% fuel. Keep the CG low in the hull as well - It'll be plenty stable in the straights, and still turn very nicely.

BTW- Prather did recommend the 40" hull for .45 to .65 engines, so you probably won't be overpowering it with a .60 air engine.

Let me know if you need any other info from the instruction booklet, and I'll look it up...

Duane

 

[crrcboatz]

If you want to go all retro, I have the hardware kit NIB and your choice of a nice modded Speed Webra marine either 40 or 61. Both were pretty hot for their day and have almost NO time on them. If face Glen Dye did the mods on the 2-61s and the one 40. Would be truly a nice retro with this stuff.

Curt

 

[topfuel443]

Erin, just put the old power plant from Project Hydro Plow in there and let 'er rip!

This is gonna sound weird, in fact it is weird. I was doing some serious brain planning last night about a single tank/double chamber fuel cell for my twin, and low and behold, I have a dream about your old boat. I remember the pics of the two separate tanks set up saddlebag style. That was a long tim ago...!

~James

 

[Propjockey]

Outstanding Duane...I appreciate it! Any mention of how deep the prop should run or it's location fore/aft?

Curt...you've got PM.

James...James...James. Does Meghan know you're having dreams about me? :huh:

Hydroplow was the ultimate excersize in futility, wasn't it? Hey kinda OT, but what do you know about EFI on motorcycles?

 

[topfuel443]

Shes not here thankfully....lol And it wasnt about YOU! just your boat...dont know which wouldve been weirder...

What do you want to know about EFI? wouldnt want to clog up the thread, but its yours, so fire away.

~James

 

[Propjockey]

LMAO! I'll shoot you a PM.

 

[crrcboatz]

depth of strut is about 1/2 to 5/8 center of prop shaft to deepest portion of the vee on the transom I think I built a 46 years ago and that was the setting I think.

I also have a complete 46 prather NIB original box with cowl, all hardware in original box, with flex shaft, and extra gas rudder for sale.

Curt