Surface Piercing Props

There seems to be a lot of discontent with fixed SP drives in particular,and surface drive in general.Some say that 30-40 knots is a must to use the advantages,some are running at a lesser speed and would not make it to 40 knots.If a boat is not going to be used mostly in the efficency range of SP propellers and surface drive is it wise to use that system.The same would apply to jets and their advantages and dis-advantages.Expectations are met only by experience.Surface riding props were noticed by race drivers and they tried to push them back into the water where they thought they belonged,(direct drive high rpm) until they realised more speed was achieved surface riding on prop hubs.Early SP props used by Hickman and sea sled(big props slow rpm).There is also the problem steering with fixed surface drive.

 

Very interesting thread. I own a boat with fixed surface drives. I have finally had enough of them. I am removing them and installing Arneson drives in very short order. As mentioned in above post. If you are cruising at a moderate speed they work great.If you start to jamming the sticks forward the bow drops and the handling gets very interesting to say the least. If you are docking with no wind and no current, they are not a problem. Add a few gusts of wind, or the tide is running the wrong way, you had better have a good crew. This set up can make you look like an idiot at the dock. One good thing is the fact that they are very, very, simple. there is virtually nothing to mantain or ware out. I have put over 500 hrs on these drives without ever touching them. I have also spent a small fortune on experimenting with props, ended up going back with the first set. They are set at 10 degrees. I think that that is the biggest problem. the faster you go the more the stern lifts up. You could probably go to 5 or 6 degrees and it might work well. But I think having trimmable drives will be the cats A$$. It will be a fun project. Starting on it after the new year. If I get ambitious and organized enough I will keep you posted with pictures and a narrative as the project progresses if anyone is interested.l


Steve H

 

We start the conversion from fixed surfacedrive to sterndrive in two weeks, and will finish in january. Can post pictures and results if any interest.

 

I would be very interested. What use is that boat designed for? The scenery in your pics looks very similar to the Pacific N.W. Are you staying with the Yanmar or going to smoething else. There are not any stern drives that I know of that will handle that kind of torque and live to tell about it. I like stern drives alot. What I don't like is the maintenence if they are left in the water 24/7, especially salt.

Steve H

 

Steve
We go for a Volvo D6-350hp with DPH drive.
I am in Norway.

The boat is built as a fast response craft for a 3-man diving crew. It is fittet with hydaulics for drill-hammer, winch etc. In the wheelhouse there are 3 dampened chairs, some electronics and cooking/heating facilities. We aimed at 72dBA in the wheelhouse at cruising speed, but didn't reach that low levels with the incredible noise form the surface prop. Other 30-35kts boats we have made with jet or axle have all been in the 68-72dBA range.

Design goal was to acheive a cruising speed of 33-34 kts and beeing able to keep that speed in nasty choppy fjord waves.

 

Hi jba.A much more interesting project,would be to convert your present drive to 20 degrees of trim and to fit rudders or rudder that are able to be raised for speed and lowered for docking.Fit trim tabs on rudders for 50 degrees of steering.The rudders should move independent of the drive.A simple over-christmas project.

 

Increasing the angle would compound the stern lifting problem. The rudders already come up when the stern lifts as speed increases. The faster you go the less rudder you have in the water. Not good! that is why I am going to trimmable Arnesons


Steve H

 

The suggestion was,with a trimable drive the prop can be raised right out of the water,or horizontal to the keel,or any running depth you choose.The rudders are independently adjusted.all of this would be controlled by the Electronic Engine Management System,plus sensors for shallow water and obstruction strike of the drive. This is one of the advantages and systems used in CAM.A.PROPULSION.