Fixed Propeller
Source Specification
B T Marine
Units 10 & 11
Swift Industrial Estate
Greenhill Way
Newton Abott TQ12 35H

44 (0) 16 2636 8484

Propeller No. 10472 L.H. 570x420x3

Taper 1:12 1 3/4" Shaft 3 7/8" Long

Key 7/16" Square

NVT M30x3.5

Thread Length 1 3/4"

We keep a fixed propeller just in case the autoprop fails.

Autoprop H9 Propeller

Bruntons Propellers Ltd
|Oakwood Business Park
Stephenson Rd West
Essex C015 4TL

The picture to the right is from their page. Also they have an excellent page that describes installation - I copied it below.

Regular greasing of the propeller is required - do it at least annually at haul out. To remove and/or service the H9 propeller you need the following, all available from Bruntons:

  • H9 Roller Beraing Tab Washer Kit
  • Propeller Puller
  • Nut Spanner
  • Crease
  • Peg Spanner

Installation Instructions

The Autoprop is supplied fully assembled, tested, and ready to fit to your yacht. Observing the following instructions and notes will ensure correct fitting and trouble free service.

Make a note of the AP number marked on the blades of your propeller. This is a serial number that will have all specifications of your propeller, hub, engine etc.

Tools required for installation/removal and maintenance
Selection of Allen keys (metric)
Small flat blade screwdriver
Socket wrench and/or adjustable wrench
Propeller puller… Autoprop specific puller available


Before installing your new Autoprop ensure that the cutlass bearing is not worn. A worn bearing will not be suitable for any propeller. If it is worn, replace it with a good quality bearing…preferably with a brass shell casing.

1. After removing the old propeller check that the shaft taper, key and thread are undamaged. Try the new shaft nut on the shaft thread. The shaft taper should be clean and dry. Check that the key will slide through the Autoprop keyway without jamming at any point.

2. Slide the Autoprop onto the shaft (without the key in place). Mark the shaft at the forward edge of the Autoprop hub. Remove the Autoprop and place the key into the shaft keyway. Slide the Autoprop back onto the shaft and check that the forward edge of the hub comes to your shaft mark. If it does not then it is likely that the key is too large, and the Autoprop is not seated to the shaft correctly. Remove the Autoprop and file the top of the key down until the Autoprop will slide on to the shaft and reach the mark. This will ensure that the Autoprop is now correctly seated to the shaft taper.

3. Screw the new shaft nut up tight on to the shaft. In some cases the flat on the nut will be positioned so that the locking screw will tighten directly to the flat. If the locking screw hits on the barrel of the nut then it will be necessary to dimple the shaft nut with either a drill or punch. (See Figure 1 for examples).

4. Smear the threads of the locking screw with thread locking compound and screw it down on to the shaft nut.

5. Re-install the anode nose cone on the aft end of the propeller hub.

The installation is now complete and the Autoprop is ready for use.


1. We recommend that you use the Autoprop puller or similar when removing the propeller. This puller is simple to use and avoids having to remove the rope cutter if fitted. Most three legged prop pullers will also work with the Autoprop.

2. Remove the anode nose cone by removing the three nylon screws.

3. Unscrew the shaft nut locking screw until it is clear of the shaft nut.

4. Unscrew the shaft hut.

5. You can now use the puller to remove the Autoprop from the shaft. If using the Autoprop puller attach the plate to the aft end of the propeller hub using the three threaded holes for the anode. Screw in the center-jacking bolt until the propeller hub loosens on the shaft taper. Remove the propeller.

6. Tape the key to the shaft or remove and keep in a safe place. Generally the key is supplied with the shaft… not with the propeller.


Your new Autoprop is fitted with greasing channels in each of the blades. Therefore blade removal is not necessary in order to re-grease the propeller bearings.
The Autoprop should be re-greased once every two years or if more convenient during your annual haul out.

The Autoprop needs good protection from electrolytic and chemical corrosion. Ensure that you replace the anode when ever necessary. Early dissolving of the anode could be an indication of an electrical problem within the boat.
For additional protection it is advisable to have a shaft anode, as the Autoprop anode will only protect the propeller.

While in the water the Autoprop should be cleaned so as to obtain optimum performance when motoring. Heavy fouling of an Autoprop (or any propeller) will reduce the propeller's performance. With heavy fouling there will be a loss of thrust and also a reduction in the maximum engine RPM attainable. (This will also happen with a standard propeller.) The Autoprop will still self-pitch correctly.
In areas of high fouling, smoothly coating the Autoprop with a high quality marine antifouling may help reduce the growth.

Whenever you haul-out for antifouling or laying-up for example, the Autoprop should be given a power wash, before it dries out. This will remove any deposits or growth from the propeller. After this rotate the blades by hand to ensure that they move freely.
If you are leaving the boat out for a longtime it is recommended that you re-grease the bearings at this time.

Greasing the Bearings

There are two 5mm stainless steel pan head screws in each blade. One in the center of the blade bearing cap, the other in the base of the blade. Both are fitted with "O" rings. The one in the center is the grease exit hole. The one in the base of the blade is for inserting the grease. Both will be removed during the re-grease operation.

A special grease fitting is supplied with every propeller. This fitting will attach to a standard grease gun hose end fitting.

Only use the recommended grease or one with the same specifications or better. Two recommended greases are SKF LGWA 2.0/4 or CRC #SL-3110, New Generation.


1. Using a 3mm Allen key remove the two pan head screws.

2. Screw the custom grease fitting into the channel on the side of the blade.

3. The blade can now be filled with new grease. Pump the gun until new grease pushed up out through the exit hole in the center of the blade. Rotate the blade to ensure all of the old grease has been removed.

4. Clean any excess grease from the retaining cap and replace the pan head screw and "O" ring.

5. Remove the grease fitting from the side of the blade and replace the pan head screw and "O" ring.

6. Ensure that all three blades have been done and that all pan head screws have been re-installed.

Bearing replacement

Being a mechanical product there will come a time when the bearings will need to be replaced. This is a straightforward procedure. It is not necessary to have the propeller sent back to Autoprop to have the bearings replaced. Any good facility will be able to do this.
Full instructions are supplied with the bearing replacement kit. To order this kit, simply contact your Autoprop distributor with the AP serial number. They will know the correct kit to supply.

Additional Information: Automatic Variable Pitch
The Autoprps blades are custom designed for the particular power, shaft RPM and speed of your yacht. The components of hydrodynamic force (boat speed), and centrifugal force (SRPM) balance, to set the blades at the correct pitch angle. As the yacht speed or the engine revolutions change, the blades will automatically re-adjust to keep the optimum pitch angle to the waterflow. This gives a high thrust and efficiency over a wide range of conditions.

Feathering your Autoprop under sail
All you need to do is to stop the engine while motoring in ahead, this will feather the blades. Now leave your engine engaged in ahead. This applies to mechanical transmissions.

If your transmission is hydraulic you will need to have either a shaft brake or shaft lock.

Maneuvering Characteristics
Due to the self-pitching action of the Autoprop, maneuvering is different to a conventional propeller. Firstly, in most every case, there is noticeably less prop-walk experienced. This is due to the finer pitch setting at low speeds giving a reduced "paddle wheel" effect. Secondly, in reverse the blade shape is exactly the same as in forward. Thirdly, due to the finer pitch, at low speeds there is less "bite" felt when engaging ahead or astern from a standstill. This means that more engine Rpms than normal should be used when moving off from a standstill, or at very low speeds. Once some speed has been attained, the engine Rpms can be reduced.

Ed. Note: NOT apparently the case with the Challenge 72! Prop-walk is quite pronounced on Ironbarque.

This unique feature of the Autoprop enables the full power of the engine to be used in situations such as towing, or in emergencies. With conventional or feathering propellers, the pitch is too coarse at very low speeds, the engine cannot achieve its full Rpms, and therefore full thrust is not achieved.

Damaging your Autoprop

The Autoprop is some 40% stronger than conventional propellers, as it is made from a special high-grade bronze alloy called Superston. The high resistance to impact damage means that you are less likely to damage the Autoprop blades. In the unlikely event that a blade becomes damaged, you only need to replace that blade, and not the complete propeller.

Fitting a rope cutter
You may fit a rope cutter with an Autoprop in the same way as any other propeller.