Propeller "Science" is confusing.
 

I am buying a boat now and we are going to transport the boat but it does not have propellers.The boat is a ocean express cat with twin arnesons.
I was hoping to talk with Bblades I sent them a message but how do you calculate what kind of propeller and not get one too big or to small right pitch and diamter etc...

Anyone can share their knowledge of prop "Science" ....?

Use the BAM prop calculator, you can do it for pitch or speed, as long as you know, Weight, Ratio of drive and speed it should do. It will work backwards and give you pitch. But then you'll need to figure out Diameter and Rake.
Just keep buying props until your garage is full. Finally get it right and sell the Boat!

Buy a big prop and keep adding HP untill it pulls it easy.

Also call Rik at Arneson. He should be able to get you in the ballpark

turbo,

I looked for your message and couldn't find it anywhere.
Ocean Express Cats typically like large diameter propeller. We tend to set them up with inward rotation but outward is old school standard and it will depend on your goals.
If you supply me with wet weight includinf people, gear, fuel etc., I can get yu very close on propeller geometry to start with. Ultimately, a baseline test with a set of props will point you in the correct direction.

Here is a link to BBLADES prop slip calculator. It is a useful tool but will not give you the answer you need without other factors being determined.

turbo,

I looked for your message but was unable to locate it anywhere.
Ocean Express Cats tend to run large diameter propellers. We often turn the props in on these set ups. However outward rotation will be determined by the boats personality and your desire.
Ultimately the geometry of the props will need to be decided with a baseline test. I can come very close to a the initial geometry if you supply me with a accurate wet weight including fuel, people gear etc. I will also need the true HP.
Here is a link to BBLADES slip calculator. It is a useful tool but will not help you get the full answers to your questions.

BBlades Propellers | Prop Slip Calculator

Brett

I have a pair of Number 6, Hering 5 Blade, 18 Diameter, 18 Rake, 28 Pitch Props I might sale. Also, a pair of number 6, Mercury, 4 blade, 17x30 pitch. The bad thing is that I need to sell both of these so I can buy a new set. If interested, call me. I will think about it. Leave message. I will not pick up the phone if you are not in my contact list. 281-743-5390

Hello Bret, can you help me to decide which propeller I need.I sent you 2 emails.Or is there anyone else who is good to determine the right propeller for a application I can not use the boat because we do not have propellers

Sorry for the delay. I'm responding to your email now.

Also so you know the gear ratio is 1.1 not very excited about that but it is true