Surface Piercing Props

[gyrojocky]

Greetings.
My brother and i are building 3 alluminuim power boats and want to experiment with our own surface drive units for them. Its proving very difficult to find out about propeller sizing. We downloaded an article on S P Props by
a Paul Kaman which was very interesting and that had a link to a prop size calculator for S P props, but the link is long dead and we can't contact Paul.
Can anyone help us ?. There must be somone who knows about these props and can advise us how to calculate a starting pointso we can order one, i guess we won't get it right first time but must start somewhere.

Many Thanks. Ken

[Ilan Voyager]

I think that the link you're searching is http://www.well.com/user/pk/SPA.html for downloading the soft (power.zip).

You have also http://www.francehelices.fr/ who makes a surface drive and lot of propellers.
The page http://www.francehelices.fr/surface-drive-system-uk.htm describes the surface drive and props.
The page http://www.francehelices.fr/france_h...lculations.htm has on line calculators that can help you.

[gyrojocky]

Thanks Ilan.
For the info i have downloaded the calculator, though on viewing it i think it is for to complicated for what we need as we are not interested in getting raceing speeds. Our top speed hope is around 30- 35 mph. The boats will weigh in at about 1300 lbs with just under 20' waterline and a 19 degree
deadrise. we are at the moment thinking prop size of 18" x 22- 24 pitch. We are enquiring to the link you supplied for this. Do you ( or any other reader ) know of any other surface piercing prop makers we can enquire to.
If any other forum member has any coments on this project please reply by forum or email.

Ken.

[tom kane]

http://www.well.com/user/pk/SPAprofboat.html Surface-Piercing Propellers by Paul Kamen,NA is an interesting article

Don't forget the possible vertical lift you may experience from the sufrace props. You hull effiency may be poor if you can't get the bow up and out of the water. I recently finished a 30 deep-V alu workboat with a fixed surface drive. It did 32kts and trimmed perfectly at 50% engine load and 36 at max power with a heavy bow plow. Lcg is about 15% aft of midship waterline. I can post some pictures showing trim at different speeds.
We are now going to throw out the surface drive and install a jet or sterndrive.
post@innovation-as.no
JBA

[DGreenwood]

JBA - Before you throw in the towel on surface piercing. Are you aware that a good prop builder can help reduce or increase verticle lift?

[tom kane]

Jba. With CAM.A.PROPULSION you can have the choice of running as surface drive,or as sub-surface drive,and many other configerations such as jet,turbo,Kort nozzle,steerable or with rudder,or out drive configeration.All from one motor instalation.If you change your mind,it is not expensive to swap over.

DGreenwood, we tried a number of different propellers that should fix the problem according to the drive system vendor. Traditional cleaver styles with cup, one where the cup was removed on the inner half of the blades, round tip, with and without rake etc, and the latest prop we tried before the decision to throw out the drive was a round tipped 4blade 23x28 with round tip and lot of rake. The boat then did 35kts at top and still 32 at cruise, no noticeable change in trim.

JBA

[JBAInnovationAS]

Some pictures of the boat in question. The stern lift really kicks in at 32-33kts.

[gyrojocky]

Thanks for the info JBA Please tell me what size engine and what size prop you are running, Also at what angle is the drive to the keel ?.
Thanks Ken.

[JBAInnovationAS]

Boat details:

Loa: 35'
Lwl: 28'
Bwl: 7'6"
Displ running: 9-10000lbs (the speeds below are actully at just below 9000lbs)
Engine: Yanmar 6LY2 420hp
Gear: ZF280A, 1.77
Drive: Fixed, 8°.
LCG: approx 15% aft of midship Lwl, trims approx 1.5-2° aft when lying still.
The hull is a monohedron 23degree V bottom.
Prop: 23x

Have tried 23x31, 22x28 and 23x26 cleavers, 23x28 and 23x26 round tip without rake, and a 23x27(or28) more like a chopper style with round tip and a lot of rake, all 4-blade NiBrAl. The chopper prop with rake was supposed to eliminate stern lift from the drive, but we didn't notice any difference.

The only difference between all the propellers were engine RPM and a minimal change in top speed, all props produced around 35-36kts.

Some inputs I have got:
* 8° is not suited much above 30-33kts.
* A single (large) surface prop may work better on a heavier boat with less deadrise and more longitudinal stability.
* The prop diam and gear ratio is wrong, should have a 5 blade with less diam and less pitch, and higher prop RPM.


JBA

[gyrojocky]

Hi. JBA.
8 Degrees seems like a very large angle it will push the nose down while trying to push the transom up. We were considering 3 or perhaps 4 degrees but now you have mentioned this problem maybe even less is better ?.
Gyrojocky.

[D'ARTOIS]

A costly affair, to experiment with surface piercing props. Only applicable to vessels with specific purposes: Off shore Racing and the like. There are a few manufatureres like France Hélices, Rolla (bought by Lips) also ZF is going into this difficult market with only a few customers, like Pershing, Azimuth and Sunseeker for their larger yacht series.
What do you plan for? A Levy type propulsion system or a SDS type?
It gives fantastic speed but very poor manoeuvrability at low to zero speed,
since you have no pressure on the almost non-existent rudder(s). Specifically for the larger yachts, it requires a very skillful helmsman.
No design for beginners!
Regards,
D'ARTOIS

[nevd]

What is the trim angle of the keel at each speed and can you solve the stern lift problem by moving LCG aft? I ask the questions as trim does not appear excessive at 31knots and moving LCG aft will be much cheaper than converting to another drive.

[JBAInnovationAS]

We have tried with as much as 500-600kg (11-1300lbs) at the far aft of the deck, that is about a meter behind the stern of the hull. It may not show very good on the pictures, but the aft deck protrudes about 1.3m over the drive unit. This was also done to effectively move the LCG aft.

The weight didn't make much difference, maybe the boat trimmed a little better up to 34kts, but still trimmed hard nose down with full power. If the LCG was any further aft than this, we would be having trouble with getting the boat on to plane, and we would get a bow that bounces sky high in every wave.

We have now made the decision to go for a Volvo D6-350hp with DPH drive.
A lot less horsepower, but we should get perfect trim with the sterndrive. Also, the efficiency of the Volvo duoprop should not be wery poor in this speed range.