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Frequently Asked Prop Questions.

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Old 07-10-2013, 02:42 AM   #1

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Default Frequently Asked Prop Questions.

Here's a compilation of some of the most frequently asked questions about props and my thoughts in response. I'll add to these as i think of them. Again, please note that there are always exceptions to the general rules on Props so you dont have to agree with me...

Which prop will give me higher top speed and better low end acceleration?

This is a non-starter. It aint gonna happen so get it out of your head now! Using a lower pitch prop, or a 4 (or 5 blade) prop of the same size, will improve acceleration but always at the cost of a lower top end. Increasing your prop pitch and dropping to a 3 blade prop will usually improve your top end but at the cost of less (sometimes poor) acceleration out of the hole. Figure out which you want for your boat or find a happy medium. Better still, have 2 props available and use depending on your plans for the day.

Should i repair my prop or buy a new one?

Generally minor damage (bends/dings etc) in an aluminum prop can be repaired for a reasonable price. If you decide to repair, make sure the shop does not file down the blade edges thereby reducing diameter. If your damage includes bites or chunks out of the bade, you should consider a new prop.

Remember that while aluminum propellers can be welded back to look like new, there is significant loss of strength when you do. It wont take much of an impact to cause further damage to your aluminum prop and on that basis i wouldn't spend more than $75 on repairing your aluminum prop when you can buy a new one for $125-150. Stainless props do cost more to repair than aluminum because the stainless is more difficult to work with. However, once it is properly repaired they can be every bit as good as a new prop.

Should i pay the extra $$ for a Stainless Steel Prop?

Stainless propellers generally cost about two-three times the price of an aluminum or composite propeller. And for those of you with duo-props that can get expensive. In most cases though if you make a direct conversion to stainless in the same diameter & pitch as your aluminum prop, you will notice an improvement in both mid-range acceleration & top speed and the reason for this is simple. Stainless is approximately seven times stronger than aluminum. Propellers don't need to be that much stronger so as a result manufacturers can make the SS props thinner and still be two or three times as strong. Thinner props cut through the water easier and this of course means better performance. If you are happy with the performance of your aluminum prop then dont spend the extra money on a SS prop.

Should i buy a composite prop?

For the most part, composite props have improved considerably over the years and are now close to aluminum props in quality and performance. From what i've seen out there, Piranha probably makes the best ones and they have the ability to easily replace blades & hubs if they break. That said though, if you hit something hard enough i've seen two of those composite props completely shatter in the last 4 yrs. I've also read comments that the blades have pulled from the hub when they are overloaded when doing things such as pulling tubers with V6/V8 power. Personally i think they are good as a spare prop to be kept on board in the event of damage to your main prop.

Should i buy a 3 blade or 4 blade prop?

This question could be combined with "how to i get my boat onto plane faster'? This one is interesting because there are many variables to consider but for the most part, If you look at a propeller from behind and visualize a circle that the blade tips would draw, you will see that the blade of a 3 blade prop covers about 50 -55% of the circle. (This is called diameter area ratio, or DAR). You can add thrust within this drive circle by increasing that percent (to say 60 - 65%) by adding a 4th blade. When you look at a four blade prop you will notice that more of this area is covered because of the extra blade. That means more push contact with the water. Think of it as going to wider tires on your car. More traction for your car and more traction for your boat. Just as wider tires on your car usually do not alone increase top speed and can actually reduce it, the same usually holds true for a four blade prop. One big advantage however, is that the added thrust from a four blade prop can keep your boat on a better planing angle in mid-range and lower RPM's, which as you can imagine translates to better fuel economy. Combine a correctly pitched 4 blade with a set of Smart Tabs and your boat should literally pop up onto plane very quickly.

How do i know if i have a spun hub?

Spun hubs are the result of the rubber hub inside prop letting go and not 'sticking' to the prop. This can be caused by age/wear & tear or impact. Usually the easiest way to recognize this problem is when your boat will accelerate slowly up to a cruising speed but if you try to accelerate quickly, your rpms shoot up fast but you dont go anywhere. In severe cases you wont even be able to accelerate slowly. For the most part, new props have replaceable hubs and make the job of replacement much easier. For those of you who are still using props that dont have replaceable hubs and suspect that your hub may have 'spun' there are a couple of tricks to check them first before you take them to your prop shop for repair. First off remove your prop and check for burnt or frayed rubber in the hub. Second, if its not obvious that you have such a problem, mark (scratch/centre punch or etch) both the hub bore and the rubber in a straight line & then put the prop back on and try it again. When you remove the prop after re-testing, check to see if the scratch marks are still lined up. If not, you have a spun hub. There is also another way to test the prop hub without going back into the water. Again remove the prop and mark both the hub bore and hub in a straight line & then put the prop back onto the outdrive. Making sure your boat is NOT running, put the shifter in to forward gear and then turn the prop counter-clockwise (backwards) until it stops. Then put on a good safe pair of work boots (not your sandals!) and give that prop a solid kick in the same direction. Remove the prop and see if the marks are still lined up. If not, take your prop to a prop shop to have the old hub pressed out and a new one pressed in. Installing a prop hub requires the use of a significant amount of force so its not really for the DIY crowd. A better option is to buy a new prop with a replaceable hub.

Hubs

While i'm on the subject of hubs, if your prop still has the old rubber hub style that is press-fit then i suggest that you change it over to one of the Flo-Torq or XHS style hub kits. Once the rubber style lets go it usually has to be replaced by a Pro with a heavy press. The other issue with the rubber style hubs is that it takes quite an impact before they release which usually means a higher potential for damage to your outdrive gearing. The Flo-Torq or XHS style reduce and even eliminate these problems. The release point is much lower and due to the design the potential for gear train damage is also greatly reduced or eliminated. And the bonus is that you can easily change them yourself. Buy a spare hub kit and keep it in the boat along with your prop wrench so that you dont spoil a good day on the water in the event of a prop impact.

And i almost forgot about this one....
Should i put a hydrofoil or fin on my outdrive?

Why of course you can. While you are at it, buy yourself a pair of Mickey Mouse ears and wear them while u are driving your boat around with that nice new hydrofoil. Just dont expect any sympathy around here when you hit something and lose half of your outdrive.

Last edited by mikeyt; 08-12-2014 at 11:30 PM.
The Following 5 Users Say Thank You to mikeyt For This Useful Post:
ledacious (11-02-2013), Michael709 (02-05-2016), rainman55343 (07-10-2013), rhinoz (07-12-2013), Triscuit (01-27-2016)
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