Wednesday, November 19, 2008


Did you know that the only outboards that come propped directly from Mercury are 2.5 hp to 15 hp engines? Surprising, isn’t it? If you purchase a boat that has an outboard anywhere from 25 hp all the way up to 300 hp, the prop was chosen by either the boat manufacturer or the boat dealer that rigged the boat. Why? Well, it’s simple really, and it relates to a previous post about finding top speed.
Remember when I told you about the fact that the same exact engine on two different types of boats will have drastically different performance specs? This can also be said for the propellers. A 150 hp Optimax engine mounted on a bass boat may have optimal performance with a 23 pitch (23P) prop, whereas the same engine mounted on a big pontoon boat may need something with a much, much lower pitch to get the RPM in the recommended range. Since Mercury doesn’t know what boat the engine is going to be mounted on, we can’t send the engines out with props already on them. Makes sense, right?
So you’re looking at a nice used boat with a big Mercury outboard on the back and you think to yourself, “I wonder what prop came with that originally…” The best place to find this information is the manufacturer of the boat. Or, if you know which dealer originally sold the rig, you may also be able to check there. But wait a minute, does that mean a Mercury customer service representative can’t help you when you’re looking for a new prop? Of course not! We just need some information from you to best help you find what you’re looking for. Here’s a short list of information you should gather before contacting us:
1) Engine serial number
2) Boat type (manufacturer, length, material)
3) Gross weight (boat, engine, gear, gas, people, etc.)
4) Current prop material and pitch5) WOT RPM with current prop
With this information we should be able to give you a very solid recommendation on what prop to try on your engine.


D. Mercer said...

After speaking with the people at Miami Marine about the correct propeller selection, My boat has performed better than ever getting on a plane faster and cruising speed has increased. I would recomend speaking to these people about props they were very helpful and courteous.


Charles Roring said...

I like reading this blog because I also write articles about naval architecture and ship design especially on the subject of marine propulsion. You can see it at the diary of a naval architect. I hope more people will understand more about ship world and naval architecture.