Hydrohellion

Hi guys I read in a previous post that for a surface drive you should drill the stuffing tube hole at 1/2" above the center of the bottom of the keel and 1/4" to the right?

Is this correct?? It is for a 54" old dumas scarab

how far back should the prop be?? I have this stinger drive that puts the drive dog 4" behind the boat, is this too far?? my rudder starts 3.5" back, they don't interfere but when turned one way the prop will get LOTS of water Should i get the rudder to sit further back?

Scott Schneider

In the case of the Scarab, it is a moderate V shape and not really too sure a Surface Drive set up is optimum ?
Generally shallow and medium V hull work best with "Semi Submerged" drive. that being havinr stuffing tube run JUST UNDER the keel and props hub just barely under water.
* If you are convinced otherwise that a surface drive is what you want, make it is LOW AS IT CAN GO !!

Hydrohellion

Not convinced at all, in fact the drive that is mounted now is aligned for sub-surface as I was going to run the Homlite engine, I decided to switch to the surface drive when i changed to the RCMK, as the motor is a high rpm motor, if you think i should keep it sub-surface then all I have to do is drill the stuffing tube.

This also places the drive dog aprox. 3"- 3.25" from the transom

How far from the rear should the stuffing tube exit the hull?

Should I still set the propshaft 1/4" to the right?

Scott Schneider

Rearward distance stuffing tube go's is a strut specific thing, tho prop being further back is a GOOD thing .
Quite frankly being your NOT building a racer, keep the drive in a "Semi submerged" configuration.
Plenty of bad azz small props that will work really well with the RCMK set up that way
VooDoo/ propshop 6516/3 - 6518/3 ... ABC 2514's to name a few of the outstanding ones.
As to the offset, No ! .... boat wont track right with a offset stuffing tube under the keel.

martno1fan

Go with surface drive plenty of scarabs running surface drive setups,theres been two new restorations on here recently have you seen them? both went with surface drives although one went with an out drive setup.
Mart

[link]http://www.rcuniverse.com/forum/m_8704018/mpage_1/key_/tm.htm[/link]

[link]http://www.rcuniverse.com/forum/m_8704018/mpage_1/key_/tm.htm[/link]

FlogginHarvey

Here is what I have learned on the Dumas Scarab so far with lots of help from this and another board (THANK YOU to all by the way):

The boat was originally designed for the submerged "oldschool" drive with a nitro and is considered a "hi-lift" hull with lots of strake and hook in the aft 25% of the running surface.

The guys running surface drives with Zennies or RCMK's are doing so with great succes and even better when the running surface is "blueprinted" or faired-in and hook removed and some even still have removed some strake as well (not me yet with the strakes).

I say play around with what you feel but you will have MANY more choices for props if you go surface drive...and a bit more "tunability" with the surface setup as well.

Most with the Deep Vees (or Monos) are using a 6" rudder standoff from a few different companies. Accutech, Speedmaster, & Top Secret are just a few of numerous popular names in RC Boat Hardware...

others run the strut/rudder combo for sport boating which puts the rudder directly behind the prop and will turn equally well in both directions Bonzi and WarehouseHobbies do the strut/rudder combo along with others I would think.

My build is the Steerable Strut (looks like an outdrive) and I am VERY excited to get this FINALLY put back together and in the water...it has been a long process but a fun one that helped me learn a TON along the way!!!

Scott Schneider

Just feeding the "Food for Thought" process ....

High lift hulls along with shallow V's hop around a lot more than deep V's at speed. When you run a SURFACE drive on them the prop unloads a lot more ! If the engine in boat is pretty high performance ? the RPM spikes it is subjected too every time the props unhooks is VERY hard on them and can lead to premature engine failures.

FYI

FlogginHarvey

Good point, Scott. It seems like every hull from Dumas varies a bit in final weight depending on how skilled the original builder was with stringer and trassom doubler install.

My Scarab is like 17lbs WITHOUT any hardware or motor...whomever installed the stringers used WAY too much resin. I tried cutting some out during the resto but it was CRAZY...oh well. It will be a GREAT rough water sport boat!

It will need a higher-lift design to help counter-act the extra weight...at least that was my original thought and why I did not make the strake mod at the same time I did the Blue-print...I am really just full of BS until get this baby int he wet stuff...

But, and this is a HUGE but, I run clutches on EVERYthing I run so far and that supposedly helps with the load variances...eh?

martno1fan

17lb oh my god thats heavy [X(] my vee i build even though its only 46" weighs 2.4 kg or 4.4 lb with stringers and plywood transom support.Why they made a 55" hull that heavy ill never understand,even a 60" hull for that matter,be like driving a brick .
Mart

darindotson

The Dumas Scarab is a semi-scale boat, not meant to be an all-out performer. The hull is so heavy in order to handle pretty rough chop. The last thing I want is to go 60 mph and flip the thing, stripping off the 8 stainless steel cleats that I just installed for scale looks. Some of Dumas' lightweight woodies are more designed for speed.

FlogginHarvey

Ran the Scarab last night and was doing roughly 30MPH and no high speed needle at all...pretty impressed with the boat (if I do say so myself) and the surface drive. I noticed a little cavitation as it was coming on to plane with the 6717/3 but seemed to run and bite great after on plane...

swapping the carb and going to re-run tonight it the weather holds.

darindotson

Thanks! I was going to ask you about the WD200 strut- how did she steer?? responsive?? I have the 7015/3 prop, I wonder how it will do with the Z-drive.

I still haven't decided on a motor- loving the Zenoah 260 with clutch from WHH, but also hearing LOTS of great things about the RCMK motor. Advice???


Thanks!

D.