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Post by nala on Mar 14, 2016 18:15:44 GMT -1
Feeling a bit better today i decided to fit the hydrofoil to my Parsun 6 hp 4stroke outboard engine....... Having fitted many hydrofoils on larger engines in the past,i thought this would be a doddle.......  Well,it was and it wasn't............it had to be modified a bit...."butchered" in laymans terms.... You'll need the patience of a saint and good eyesight....i don't have much of either... So,firstly i had to taper the front(s) of the fins as the holes were too close to the edge of the cavitation plate. I did it to the whole top and bottom of the fin (ie top and bottom of the fin groove) I could have just tapered and trimmed the top if i'd have had my thinking cap on but never mind it looks ok. Here are some photos i took of the operation...............    |
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Post by nala on Mar 14, 2016 18:18:06 GMT -1
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Post by nala on Mar 14, 2016 18:19:04 GMT -1
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Post by nala on Mar 14, 2016 18:20:14 GMT -1
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Post by nala on Mar 14, 2016 18:25:54 GMT -1
Also had to make a slot for the anode bolt to fit..... !  Job done......lesson learned.....objective is to make sure the hydrofoil fins fits the cavitation plate without having to modify them...! |
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Post by ZEBRA on Mar 14, 2016 21:28:42 GMT -1
wow thats brilliant it will be very interesting to see how it goes on the water how much difference it makes ect great report
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Post by philpot on Mar 14, 2016 22:47:02 GMT -1
Well done Alan although I must confess whilst they had an effect on one of my old 15hp engines, I found it a real pain for transporting in the car because the prop hub is now higher than the centre of the engine which means oil can run back up the shaft. Yes okay you can raise the engine head so that it is higher than the prop but a lot of faff.
I hope it is effective for you Alan but just remember to raise the engine head in the car and if this engine is a 4 stroke, they are picky with how they are laid on their side at the best of times, good luck with it matey.
Phil
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Post by nala on Mar 16, 2016 10:49:01 GMT -1
Many thanks......  Fins do work as they help the prop to "grip better",and gets the boat up on the plane quicker... Whether that'll be the case for this i don't know......watch this space....(hoping to cure the cavitation slip though.....?) You can even make a one piece hydrofoil out of marine grade aluminium/steel having made a template first. Then have it "custom made" and cut out on a laser cutter.(this would be mounted on the underside of the cavitation plate) And have a downward bend on each side (port/stbd) of the fins.....having a cupping effect. Creating more water to be thrust out the back............. |
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Post by philpot on Mar 16, 2016 22:51:17 GMT -1
If your sib is an air floor, you may need to try lifting the engine 10mm at a time by using strips of wood placed on top of the transom. Air floors are prone to cavitation issues with higher power engines and when I say higher power, on a small sib, this can be 10hp upwards. The floor pressure is critical so check the pressure with a manometer as the cold water will lower the pressure allowing the floor to flex much more.
Many many people have had issues with air floors and in most cases raising or lowering the engine can either help or cure the problem. The other thing to try is to place a piece of ply the full internal width of the floor by about 15''. This is sited with the wood touching the transom and below the air floor which in a number of cases stiffen the floor at the rear to prevent cavitation and ventilation.
I will be interested to hear how you get Alan.
Phil
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Post by nala on Mar 24, 2016 19:21:27 GMT -1
Apologies for the time delay............. Thanks for that Phil.... The engine is only a 6hp (4stroke)so i wont be breaking any records with it but i do understand whats happening.... I wonder if the ply could be substituted by chunky polystyrene....? (no sharp edges and will compress under pressure...) You've got me thinking.....  ?? The air floor pushes down on the inflatable keel.......the inflatable keel pushes the outer skin (this has to be kept as taught as poss'... : ) ) To stop the rippling effect...and try and simulate a rigid hull.. A possibility maybe to put in slightly larger piece(s)(snug either side of the inflated keel).....and as you mentioned right up to the base of transom and maybe half way up the boat....tapered in ratio.. It could be manufactured ........ 2 triangular wedges a left and right (port and starboard to be nautical..) This would be lighter and would certainly firm up the keel......and polystyrene floats.. Phil were wasted.......and definitely not paid enough.... Flights of fantasy today have become sober realities of tomorrow......
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Post by philpot on Mar 27, 2016 16:49:24 GMT -1
It is an interesting thought Alan. I doubt the polystyrene would have the rigidity to offer the support that is needed although with a 6hp perhaps it is not a big issue. On the Excel with a 15hp that I had, it became quite an issue.
Fillets of foam may be a good move and well worth a test for what cost is involved.
When I had the throttle open above half, I used to get a Mexican wave going on below me in the floor which would rise and fall 2 - 3'', really strange. This in turn caused water/air to transmit unequal water flow at the prop which in turn gives the effect of cavitation/ventilation. A well known fact of air floor boats but these sibs offer a fast set up and take down so some things have to give unless you fork out £2500 on an F-Rib which is out of this world in terms of speed on the water, stability, standing capability and still fit into my estate car to go home. Total set up time, 6mins but at a price...................
Phil
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