Flat bottom planning hull speed

Hi
You may remember that I mentioned putting a trim tab on the back of the boat but said to put the pivot point up about an inch up the transom. The concept is to provide ventilation for the transom and another stagnation pressure line on the trim tab. Which basically what a SINGLE stepped hull is, ie two stagnation lines, but with an adjustable trim tab, you would be able to adjust the angle to maximize the hull running attitude etc.
This would be an easy experiment, cheap,

 

What make of outboard do you and others use?

 

Capt Littlelegs
We race a D2 15hp tohatsu.

 

Hi everyone.
The new boat is finished and I would like to take this thread in a different direction.
Racing Fuel
Racing Oil
Racing spark Plugs
Additives etc

What can you recommend based on past experience? Please remember this is a 2 Stroke Water Cooler over rev'd racing engine that has advanced timing and standard compression. Also it is 15hp.

Also please let me know if you have tried something and it has not worked. this can also be useful.

 

If allowed you could increase the compression ratio and use high octane fuel and/or nitrous oxide/LPG injection!

Reduce the fuel/oil, not sure about Tohatsu but Yamaha run at 100:1 plus friction reducing additives in engine and gearbox oils.

Surface discharge plugs.

Racing reeds.

Keep engine temperature up by making sure the thermostat works properly.

Port polishing. Remove any airfilter and fit an air scoop.

Fit a slim racing gearbox.

Straight through or bored out exhaust.

Bigger engine and change the label!

 

If allowed you could increase the compression ratio and use high octane fuel and/or nitrous oxide/LPG injection!

Compression is 12:1 is that enough. We are not allowed to increase compression. Can you recommend high octane fuels?

Reduce the fuel/oil, not sure about Tohatsu but Yamaha run at 100:1 plus friction reducing additives in engine and gearbox oils.

Can you recommend oils?

Surface discharge plugs.

What is this? Do you have a brand and model?

Racing reeds.

Not allowed-sorry.

Keep engine temperature up by making sure the thermostat works properly.

Roger? Any reason?

Port polishing. Remove any airfilter and fit an air scoop.

Not allowed-sorry.

Fit a slim racing gearbox.

I can modify the outer casing. Any suggestion and or examples?

Straight through or bored out exhaust.

Not allowed..

Bigger engine and change the label!

Definitely not allowed.

 

12:1 is pretty high, you said standard compression! I'm not in your country so not familiar with what octane there is for sale there but I should imagine info is available from any other racing people.

I can't think that anything but ordinary marine/bike/chainsaw two stroke oil would be ok but check out bike racing and see what they use.

Champion and NGK make surface discharge plugs from at least the 1980's mainly for bigger engines but for your engine it depends on matching the thread size rather than any heat range so the pretty common Champion UL77V should fit. Surface discharge plugs are ideal for two strokes, have no electrode to get too hot or break off or long insulator to foul up and no gap to fix, they run clean with a long hard life and don't go wrong to lose you a race but there is a lot of misinformation about them. You also get a very slight increase in compression! One thing to bear in mind is these are really meant for electronic ignition and sometimes they don't work well on weak magneto ignition if you've got that but well worth a try or up grade the ignition.

http://championsparkplugs.com/results_appOther.asp?otherMotiveID=13264&mfid=2

http://www.marineengine.com/boat-forum/showthread.php?p=81098

http://www.ngkntk.com.br/site_ingles/direct/p12.html

A cold running engine won't give full power or efficiency due to combustion heat loss and can foul up and/or give fuel condensation problems/weak mixture. Try a slightly bigger main jet for a bit more power if allowed.

You could try better air ventilation through the cover or shroud.

Anything that would reduce drag in the water would help.

Keep the exhaust clean and smooth.