I often get asked the question by our Customers how do we know what is the ideal RPM or Speed for our boat.
The first question I ask them is, what is your intended application.
Once known, you can work out the optimal RPM and Speed combination to achieve the safest and best all round performance.
There are many factors that influence RPM and Speed apart from just the prop, but the prop is a good place to start.
Hope this helps.
Propeller RPM Formula:
Where RPM is slightly too high and you would like to decrease by 200 RPM .
This Pitch adjustment will do three functions:
1) Reduce take off ( Holeshot) slightly
2) Put the Motor in a slightly less “stressed” RPM range
3) Give a slightly higher “top end “ speed”.
Always consult with Manufacturer’s maximum
Motor RPM recommendations first.
Where RPM is known (R1)
Pitch is known (P1)
Where RPM required is ( R2)
What is the new Pitch (P2)
Where R1 is 6000
Where R2 required. is 5800
Where P1 is 9”
What will P2 be ?
6000 divided by 5800 x 9 = 9.3”
So new pitch required will be 9.3”
Therefore P2 = 9.3”
Alternatively, where you would like another 200 RPM higher to give a better take off ( Holeshot) as you may wish to tow Skiers, a Donut or just require more Grunt to get through the Bar and you don’t mind sacrificing a slightly reduced top end speed, then here is that Formula.
Where R1 is known
Where R2 required
Where P1 is known
What will P2 be ?
Where R1 is 5800
Where R2 required is 6000
Where P1 is 9.3”
What will P 2 be ?
Therefore 5800 divided by 6000 x 9.3 = 8.99”
Rounded out (9”)
So new pitch required will be 9”
Therefore P2 will be 9”
Propeller Speed Formula.
RPM divided by Gear Box Ratio ( GBR) x Pitch divided by 12 x 60 divided by 5280 x 1.6 =
X by 1.6 gives end speed in KPH.
6000 divided by 1.93 x 9” divided by 12 x 60 divided by 5280 x 1.6 = 42.39 kph.
Allow between 5-10 % for slip.
Each boat and set up will vary slightly.
The above is just a guide to establishing various requirements to assist in achieving the optimal performance from your motor, boat and Propeller set up.
This may be of interest if you are experiencing performance issues.
Recently, we have had a lot of enquiries about what is the best Cleaner/ Conditioner for Inflatables.
So we have attached a link for Island Girl Inflatable Boat Cleaner / Restorer, which is suitable for PVC, Hypalon( CSM) and Polyurethane Fabrics.
We use it and there is a bit of effort required, but the end results are fantastic.
Yes, it comes from Hawaii, but well worth the effort.
Merry Christmas and a happy new year. Thankyou to all our customers that supported us in 2017. Having a few well deserved days off and we are back on board on the 2nd Jan.
A lot of people ask me about Ethanol Fuel being used in Outboard Motors.
A picture is worth a thousand words.
The Ethanol dissolves the sensitive rubber caps and O Rings and other associated rubber components within the Fuel system and you end up with this end result.