PMB Model boats 

SIGMA INSTRUCTIONS

SIGMA 51 for 25cc gas engines

 INSTRUCTIONS WITH TRIM TABS

    

Sparkplug to transom with Zenoah should be close to 540mm (transom is the vertical part of the back of the boat).
CG without fuel 460mm. Fuel tank is between engine and radio box.
CG and strut height can vary with propeller size.. For example on the prototype with 7016/2 the strut is as low as possible and parallel, with 7015/3 the strut centre is higher at 13mm from the tip of the V and has approx 2 degrees negative.

           

Dimension A . As low as possible.

Dimension B Tube is offset 2 to 3mm to the right of centre. (starboard)

  

 
    
Sparkplug to transom with Zenoah should be close to 540mm (transom is the vertical part of the back of the boat). Fit the engine to the complete rubber mount assembly and position it where shown but do not fix in place yet. Remove the pullstart from the motor and remove the 3 countersunk screws which fix the big aluminium plate to the motor. The screws may  be tough to remove. Take out both screws from the red coil and loosely fit the coil relocator using the same screws. Turn the flywheel until the magnets are on the opposite side to the coil ( magnets are the shiny metal parts on the outside of the flywheel). Push the coil away from the flywheel and put a piece of thin card between the coil and flwheel. Press down on the red coil and tighten the 2 screws and then remove the cardboard. This will set the correct airgap between the coil and flywheel. Fix the motor mount brackets to the engine and fit the throttle bellcrank and/or bracket to the front of the motor as shown in the pictures.  Fit the pullstart using the M4 screws in the motor mount kit. Before fitting the pullstart make sure the screws do not bottom out. If they do then use some shorter screws or washers under the heads of the bolts. Bolt the rubbers to the brackets using the nuts and washers provided. The motor mount and rubbers will then fit between the wooden rails. Fit the coupling to the motor.
    The strut and rudder should now be mounted on the transom of the boat in the position shown in the drawing and picture. 
Drill a hole for the proptube in the V of the transom and elongate it upwards with a file so that the strut height can be varied. After first tests to find the best strut height/propeller the tube exit through the transom can be with  silicone sealer although many people leave this hole open.  Fit the tube is the next job . The tube should run along inside the bottom of the boat  and it should make a gentle curve up to the motor.  The tube will bend without kinking if bent carefully. Cut the prop tube to length so that it is about 10 to 15mm from the coupling but pushed into the strut as far as possible. The tube should run along the bottom of the hull from the transom and then be curved upward to slide into the coupling.  The front end of the tube near the engine must be supported.
 End of strut or stinger should be between 65mm and 100mm. We like to run it between 65 to 80mm but its not critical on the Sigma. The front end of the tube near the engine must be supported by the T- bar as shown in the pics. Do not fix the tube near the transom or it will be impossible to adjust the strut height or angle.  Cut the flexi to length, remembering to leave a gap of 5 to 6mm (not less than 5mm) between thrust washer and the strut. Do not cut the flexi too short, because it has to go inside the coupling as far as possible. The collet in the coupling may be closed up, if so then open each slit with a knife blade or something similar. When the collet coupling is tightened onto the shaft, use a lot of force. The fuel tank must be fitted behind and to the right side the engine, i.e between engine and radio box.  Racers will have their own ideas but keep the tank as far back as possible in the boat. The flexi should slide smoothly into the coupling, to be sure of correct alignment. Fix the mounting feet in position with fibreglass paste. This can be reinforced with fibreglass mat or tape if required. The inside of the deck hatch opening at the front of the deck should be cut back until the hatch fits into it. Fix the hatch down using GA8 hatch fasteners or similar at the rear. At the front of the hatch, trim the projecting part so that it slides easily under the deck. This part may need reinforcing with glass cloth and epoxy. The radio box can be fibreglassed in place or fixed to the rails with brackets. Take care to seal any holes in the radio box with cyano, epoxy or silicone (preferably cyano or epoxy). A standard size metal geared high torque rudder servo of at least 9kg but preferably 13 kg torque should be fitted on its side on a strong servo mount of aluminium or carbon angle. The throttle servo can be any standard or high speed standard size or small size. Use a 5 cell Nimh or nicad pack for the receiver.

Balance point of 460mm from the transom without fuel is critical. Do not be afraid to add some weight to the front of the boat to achieve this. 

 Turn fins should be fitted at 90 degrees to the hull bottom on each side as close to the outside edge as possible. Make sure the brackets and turn fin are very strong. Movement in this area will affect the turning of the hull.
   The trim of the hull can be altered by trim tabs, strut height or angle and rudder position. The boat will be fastest with a strut but if a stinger is used it is recommended not to use the larger stingers such as Top Secret. 

The flexi shaft MUST be removed and greased after every days running. Mercury Quicksilver grease is popular but any grease is sufficient.

Only use balanced / sharpened propellers. Using the CS23A long tuned pipe and 100 degree manifold and fix the rear of the tuned pipe with a stainless hose clip and aluminium bracket. Pipe length from exhaust flange on the engine to widest part of tuned pipe should be 330 to 345mm. Start at 345mm and shorten to get more rpm.

Take care to range check the radio before use.

For Zenoahs and other petrol engines use 1/4" flexi with 1/4" stubshaft. With the kit supplied prop the boat will be capable of 55 to 57 mph. For highest speed buy one of our special modded propshop props. To attain the highest speeds will take some time in adjustment of strut or stinger height and angle. If you are racing the boat then keep checking this website page as I will be producing additional or replacement items to aid boat stability and speed and will provide full trimming and running instructions.

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WE SHIP WORLDWIDE  email  here    Phone.  UK  07842 634090  international  00447842 634090.       PMB,  4, Harvey Court, Harvey Lane, Golborne, Cheshire, WA33RX  England.   Model boats of all types including FSRV, FSRH, FSRO Offshore,  Deepvee, fast electric, cats, zenoah gas boats.     Visa LogoMastercard LogoMaestro LogoElectron Logo  Copyright Dave Marles