meowy84

I'm relatively new to boating and have a few questions. Can anyone describe the differences (pictures would be great) surface drive and submerged drive (I think that's what's its called). Is surface drive the setup the one that gives you the large rooster tail where you have the cable and the prop is essentially parallel to the bottom of the boat and the submerged drive uses the traditional shaft and stuffing tube and the prop ends up being on an angle?

I just purchased a .40 powered older boat which has the flex cable and the prop is in a skeg (I think that's what it's called) and is parallel to the bottom of the boat. My question is this. When properly balanced and with the boat just sitting in the water where should the tip of the prop be? Should the tip of the propeller blade be level with the surface of the water or should the prop be totally submerged under the water and if so how deep below the surface of the water should the tip of the prop blade be?

meowy84

Oops, sorry for the bad sentence wording...got too excited typing the post.

wake77

HERE IS A PIC OF SUBMERGED DRIVE

CHEERS

brettos01

Hi Meowy84.
A submerged drive has the prop completly under the water even when the boat is on the plane.
A surface drive has the prop completly under the water when standing still, but only has approx 2/3rds to 3/4 of the prop in the water when the boat is on the plane.
On monos "V" type hulls the prop shaft comes out of the bottom of the hull for "Submerged drive", or straight out of the transom for "Surface drive".


Hope this helps you.

Regards Brettos.

meowy84

Thanks for the info guys. My boat has the same setup as wake77's boat in the picture, so it's a submerged drive. I assume wake77's boat has a cable for the drive? Also, what is the ideal submersion of the prop on this kind of boat when at rest just floating in the water (i.e. how far below the surface of the water is ideal when doing the fore/aft balancing of the boat)? And finally then, the boats with the solid shaft and stuffing tube where the prop comes out the bottom of the hull at an angle is also submerged drive?

Now, this might be too broad of a subject but what are the advantages/disadvanteges of the submerged drive systems (the flex cable versus the solid shaft) and also what are the advantages and disadvantages of surface drive. If the prop on a surface drive is so far out of the water doesn't that reduce the thrust since the prop is churning air as well as water instead of just pushing water?

Thanks in advance.

brettos01

OK Meowy84, here goes.

Usually on a mono hull, with the prop under the boat, the prop has approx 1/4" clearance from the hull.
If the prop is behind the transom as shown in the pic, it is adjustable and you need to use the old try it and see method.
No matter if if the shaft is solid or flex, if it is under the boat it is submersed all the time unless the boat is airbourne.
A flex shaft gives you the advantage of you being able to bend it to change the angle of attack by the prop.
This helps to fine tune your boat.
If your boat bounces on the water at full speed, simply bend the shaft down, this will push the bow down.
If your boat won't come on the plane, you can bend the shaft up, this will push the bow up.
With a solid shaft the only way to adjust the props angle of attack is to remove and re-fit the shaft after some filling of the hull exit point. "Messy".
Also a flex shaft is supported along the full length of the shaft tube but a solid shaft can have a bearing either end of the shaft tube and is unsupported between these bearings, this allows the shaft itself to bow in the middle which causes vibration, vibration causes friction, friction reduces performance.
And that is all the advice I can give at this point.

Regards Brettos.

Ron Olson

My Feedback: (1)

With a surface drive, it allows the prop to spin faster as it isn't fighting the water as much. The roostertail is a cool side effect. Setting up the surface drive has to be done right though otherwise you can get a lot of cavitation and/or chine walk (the rocking of the hull side-to-side).

meowy84

Thanks guys for the good info.

wake77

Long story short – speed versus efficiency.

Submerged drives come out of the hole like a ******* because of the prop/water interface but the faster you go – the more drag. Therefore, are considered more efficient overall.

Surface drives don’t (for the most part) come out of the hole worth crap because of the mount height and the blade design, but, the faster you go the harder the water/prop interface becomes and therefore the faster you go the more efficient they get. Typically, a surface prop runs with approximately 1/3 of the prop diameter in the water. You’ll notice the blade design is fatter towards the outer edge for this purpose. Therefore, are considered less efficient overall for general use.

NOTE
The surface prop can be made more efficient if the vertical height of the drive can be changed on the fly along with the trim angle. This allows the prop to be submerged during take off and pulled back up once up to speed. Large ships that need to go fast will use jet drives to get them going and Arneson surface drives take over once speeds are up (two completely independent systems).

Hope this helps.

Having said all of this i'm going to change to surface drive next summer and experment with that!
Took all summer to convince my self to get that boat up to a great speed! without to many tweaks.

I would definatly stay with a flex cable, this allows the "set up" for easy changes!

have fun!

C.

WO

Wake:

Would this sub surface be appropiate for my sv 27 36"? Warren