Re: Prop Slip Explanation
May I pipe in prior to this thread being closed??? It is my belief, perhaps wrong...... but in more real world senerios, it really doesn't matter what percentage of "slip" is or isn't happening. OMC, as an example, usually made most of their 3 cylinder ,V4 and V6 gearcases with a gear-ratio that would allow (for most recreational and fishing boat hull applications) a prop selection in roughly the middle of the available props that they happen to make. ie: most 17, 18 or 20 foot hulls will "usually" use somewhere in the 17,19 or 21" pitch props. This is fairly true of Mercury also. In order to "adjust" rpms/speed (while staying within the rpm range of the engine) you just select a pitch size lower or higher than the one you currantly have. If you are running a 19" and you are in the middle of the rpm range, you jump lower (17") to get more rpms (and "hole shot").You usually have to give up top-end speed but that's the breaks! Remember that changing pitch may also change the diameter (17,19 and 21" props may have slightly different bigger or smaller diameter but you do not have a choise of pitch AND diameter so you go with the pitch choises you want and live with the diameter you get! Lighter hulls with more horsepower will generally move you up to higher pitch props and larger and heavier hulls will move you down in pitch , generally speaking! What I've said just now is what most of us already know! But I think some people are getting confused. Now, here is the clincher!!! You cannot adjust slip, it just IS!!!!!!It makes no difference to you or anybody, what percentage slip you have!!! You cannot change it !You can change the performance of the prop and of the hull and vary the slip, but you are not really adjusting slip, it just goes along for the ride! If you really want to know what the numbers are....... well,OK, figure them out, all you math experts with your calculaters. And then you'll really have useless info that you can not do anything with except brag about to the boys down at the bass club!!!But really, it's a tried and true method of rigging a boat, with a particular motor, and a fairly common prop and then by trial and error, switching from one pitch to another, various pitches, aluminum vs. stainless, high rake vs cleaver, blah, blah......... With all the props that Mercury makes, is anyone going to just buy a $600 prop based on what the theoretical speed should be based on "slip calculations"!! No! You're going to ask your local knowledgable dealer what prop you can buy/test/return/switch untill you get "in the ballpark" of what you want/need/are will to spend/he's willing to order!!! Mercury makes probably about 200 or more different props for a V-6 engine. Now that's confusing!!!!Try to pick just one, for your money! My point is.... let's not get too hung up on slip when for most of us... it does us no difference. For those who like cutting hairs, go for it, but the real world is not about percentage of slip that you may or may not have, but keeping the engine within guideline of how it wants to run and how you want to use it!!! That's my story and it's changing minute by minute!!.... PS, I'm sure proud of you for getting along so well with each other!! Let's not loose our sense of humor.
