What size for a C30 3-blade w/Univ 5411??

[Steve Franklin]

Currently I have a 3-blade 12X9. Doesn't seem to push the boat real well--nowhere near hull speed. I can get a 20X16, but I don't think it would quite fit. Might cause a little vibration as it chews it's way through the hull. I know it would stop eventually, but not quite what I had in mind. I want to keep the 3-blade, but should I get a larger pitch? What's the right size for the 5411?Thanks for the advice!!

 

[Tim]

Not so fast....

Steve,Don't just buy yourself a larger/higher-pitch prop thinking that will solve your problem.Proper prop size is determined by several things: displacement of the boat, horsepower available, gear ratio of the transmission, and to some extent waterline length and beam (I believe, since they ask you this when specifying a prop).If you are not reaching theoretical hull speed, you probably have an engine which is underpowered for the boat (common in older boats and maybe some new ones??), a fouled bottom, or poor paint finish causing excess drag. Don't expect to reach hull speed in a seaway either, those darn waves just slow you down!Check out www.ab-marine.com for Flex-O-Fold propellers. They have a neat prop calculator right on the site that will tell you what the right size is for your exact boat. You will need to know the items I mentioned above. While you're there, consider getting yourself one of those folding props too. I bought a Flex-O-Fold myself and love it!Good luck!Tim

 

[Steve Dion]

Guestimates don't work.

Steve:Steve is correct, this is not something that you guestimate. You should contact someone that is in this business and give them you information. Many of them will know some of the critical information based on knowledge of your model.If you want an good prop guy to talk to call Bay Props in Alameda, CA. Talk to Bob Kilian and have him give you some advice. (510/337-9122) He has a process that puts winglets on the prop and cups the blades. This process makes the boat back straight and give a two bladed prop many of the characteristics of a three bladed prop. When he does this to a three bladed prop it just makes them better yet.

 

[Steve Franklin]

I say again...

I don't want to appear unappreciative, but I've read the books and studied a bit of prop theory, so now I'm looking for very specific information based on experience. My brain is full, so PLEASE...no more theory!!! What SIZE prop??? I know lots of people are very intelligent re: what considerations must be given to chosing a prop, and have done a lot of experimenting (spent a lot of money) with different sizes. All I wanna do is "mooch" off some of that experience. I'll even trade info on my experience replacing the keel stub and engine logs for SPECIFIC SIZE information about props. Any more theory about props and I'll pull out what VERY little hair I have left. (Being genetically cursed with loosing the padding on top of my head can be a real pain, but that's what hats are for, I suppose.) Whew!!! So...does somebody...anybody...out there have a Catalina 30 with a Universal 5411, pushing a 3-bladed prop that they are happy (or at least happy enough) with. Thanks for your help and listening to the rantings of someone who is covered with epoxy and knee-deep in wood and fiberglass dust. Thank God I love to sail!!

 

[larry w.]

props; no theory

steve; I don't know any theory, but I had a c-30 w/5411 that turned a two-blade folding prop. i don't remember the size, but it worked well, and most inportant, it gave me almost a knot speed advantage. with a little planning you can use the prop walk to your advatange.