Another prop question

[hbrady]

I recently purchased an 18' Crest Pontoon boat with a Suzuki DF50 outboard. So far I'm pretty happy but I have been less than thrilled with my boat's top end speed. If I run the boat with 1 other person I can get 18MPH at 6500RPM but if I add 2-3 adults my top end drops to 15MPH.<br /><br />Last weekend I bottomed out (shame on me) while navigating the shallows into my slip. One blade got a little folded over (16th of an inch), I have not noticed any performance issues but I figure it would be a good idea to pick up a spare prop.<br /><br />My question is this, what type of propeller is going to give me a more sustained top end (with load). The dealer said I'm waiting my time because I won't see much (if any) performance improvement with a "performance" prop. Do the 4 blade designs help sustain top end at all? I was looking at Four-blade Comprops.<br /><br />Any suggestions?<br /><br />One more dumb question.... How do I find out the diameter and pitch on my prop? Is it stamped on the prop itself?<br /><br />-Henri

 

[Bass Runner]

Re: Another prop question

Four blade props give you more hole shot but more drag a top end, If you are running shallow water you won't like composit props the blades break easy, I would look at stainless props, and you need more pitch if you are turning 6500 rpm, if you are running a 11 pitch prop you will need a 15 pitch prop to get the rpm down, if you keep running 6500rpm you are going to be looking for a new motor, check your manual and see what the max operating rpm for you motor is and what pitch your prop is, a normal rpm for most motors is 5k to 6k rpm. If you go up in pitch from 11" to 13" you will loose 350 to 400 rpm.

 

[hbrady]

Re: Another prop question

Thanks Bass Runner! This is my 1st boat so I'm a novice at this outboard stuff. If I go to a 13" pitch and lose a few hundred RPM will I lose top end speed too? My DF50 is rated for a max RPM range of 6500, I generally run 6300-6400 only when crossing our lake (15-20 minute ride). I was looking at a Hustler aluminum prop too. I'm thinking I can get 2-3 aluminum props for the price of one stainless.<br /><br />-Henri

 

[Dhadley]

Re: Another prop question

As you go from aluminum to composite to stainless keep in mind that different props run at different engine mounting heights. It depends on the technology built into any given prop. Generally speaking a 4 blade will run higher than the same design 3 blade prop.<br /><br />You are also fighting hull design. Its typical for pontoons to have a lot of wetted surface or drag. Some designs are betetr than others. Thats, most likely, what your dealer was refering to.

 

[BrianW]

Re: Another prop question

I don't claim any expertise, but the local thought process around here, is that 'bottoming out' (or striking debris/rocks), combined with stainless steel props, causes more serious damage inside the engine. I personally would never recommend a stainless prop as a damage protection measure. In fact, I'm switching from stainless to composite due to the fact I recently hit a small log with my stainless prop and bent the prop shaft. Yep, the prop is fine, but at much cost to the engine internals.<br /><br />Your mileage may vary...

 

[walleyehed]

Re: Another prop question

BrianW, on all of our State Parks and Rec. boats, we ran ONLY stainless because we learned early-on, the stainless props kept coming back for more.<br />We run outboards for 4 years and buy new. In that time period, we may slip 1 or 2 hubs, but ZERO lower unit problems.

 

[quantumleap]

Re: Another prop question

Most of the reported damage to lower units when running stainless props would have likely still occured even if the prop was aluminum. One of the most un-true ongoing urban myths of S.S. props IMHO.

 

[jim dozier]

Re: Another prop question

Bassrunner, Hbrady is running a Suzuki 4-stroke and most of them have a higher WOT rpm (they need to turn more revs to make equivalent power than a 2-stroke) than a comparable hp 2-stroke. His issue is prop material not prop pitch.

 

[rickdb1boat]

Re: Another prop question

hbrady <br /><br />Just so you know, your speeds are not out of line with the 50 HP and an 18' toon. I would not expect much over 18-19 MPH with that set-up. I have a 70 HP 2-stroke rude on my toon and I get about 23-24 mph. When loaded heavy, this drops to around 19 or so. Pretty normal for a toon. That's why when you buy one, always get the largest motor the boat will handle. On a toon though, you will not gain much speed, but it will pull better with a load on. Just my experience over the years with a couple of toons... A stainless prop is not gonna get you much more than you have now. Maybe a mile or two difference an hour, if that. I would stick with the Aluminum personally...

 

[BrianW]

Re: Another prop question

It may be a myth, but I wish someone would tell my broken lower unit. Strangely enough, when I bent my aluminum duo-props (different boat)the outdrive was fine...

 

[walleyehed]

Re: Another prop question

Here's one....An aluminum prop (soft material) has a ding on the leading edge of one blade...lets say that ding is 1/2" long and 1/8" deep.<br />As this prop travels through the water, that ding is causing cavitation on a portion of one blade, and that blade is not pulling the load of the other 2...It sets up a static, dynamic and harmonic imbalance that takes the lower unit gears out without hitting anything!!!<br />If an aluminum prop has ANY dings, chips or imperfections in it, it is worse than running any stainless steel prop.<br />Remember, the blade shape and leading edges NEED to be near-perfect to create a "Balanced-running" prop.<br />Aluminum props are the worst because they are soft and easily damaged and owner/operators that don't understand an imperfection and what just a little damage to a prop can do to the lower unit, usually find out the hard way....this is another major disadvantage of aluminum and is also common to "most" of the GENERAL boating public.

 

[BrianW]

Re: Another prop question

A static imbalance has probably never hurt a single lower unit. <br /><br />Yes, of course damaged aluminum props cause problems, and so do damaged stainless props. Would you like to see my dinged stainless prop? I could take a picture. <br /><br />Is anyone here willing to state that stainless props tranfer less of the energy from striking an object, than an aluminum prop?

 

[walleyehed]

Re: Another prop question

Static imbalance can and will hurt your lower unit over time...do you think a side load on the shaft to the heavy blade, has no effect???<br />My point of ss vs. alum in damage cases is ss is less likely to show little bends, nicks etc., which cause greater problems later that aluminum is common for.<br />Yes, I will say there is no more of a transfer of energy in ss than aluminum.<br />Depending on the object you strike, ss is more likely to cause less damage because of momentum.<br />If you're talking about running in rocks, yea, you need to stick with aluminum, or learn how to stay out of them.<br />If you torn the blades clear-off the stainless prop, you have accomplished what few have done.<br />I can assure you the hub is spun if you torn a blade off, and in no way did it do anymore damage than an aluminum prop would have done if the drive train was is good condition before the strike.

 

[BrianW]

Re: Another prop question

Kenny,<br /><br />By 'static' I meant not rotating. <br /><br />

If you're talking about running in rocks, yea, you need to stick with aluminum, or learn how to stay out of them

Stay out of them? I live in 'em! <br /><br />Here's a couple pictures of the entrance to my favorite shrimping area. The first was taken at low tide, and I go in at high slack (which doesn't last long!) but you can get the general idea...<br /><br />This is looking into the entrance, with the current rushing out to sea...<br />

<br /><br />...a couple hours later, this is the bow view of the same spot, only I'm heading out myself, and the current has switched directions and I'm fighting it to go forward...<br />

<br /><br />But, the shrimping is good back there!<br />

 

[BrianW]

Re: Another prop question

This is my buddy cast netting for herring. The water is white from herring...uhhmm, well..., sperm to be exact. The depth finder was reading between 3-10ft but that close to shore the rocks aren't really marked on any chart...<br />

<br /><br />...but getting enough bait herring for for the rest of the year is well worth the risk. We filled several of these barrel halfs...<br />

<br /><br />Some days, when out camping, the 15ft tides are just too much to deal with, and the boat ends up 'high and dry'...<br />

<br /><br />BTW, as an 20 year helicopter mechanic, I have a fair idea of what 'sudden stoppage' means to rotating parts. That doesn't infer that the parts don't continue to rotate, but for a split second the parts do in fact 'stop' and that's not good for any system of gears. <br /><br />Thanks for your input, it's been very helpful!

 

[BrianW]

Re: Another prop question

Hit this log with my old boat, which was running a new V/P Duo-Prop and aluminum props...<br /><br />

<br /><br />...but it missed the outdrive.<br /><br />Here's a couple unusual pieces of 'debris'...<br /><br />

<br />

<br /><br />...a couple Blacktails swimming between islands. No, I didn't hit them.

 

[BrianW]

Re: Another prop question

Okay, there's some benefits to staying away from the rocks, in about 400ft of open water...<br /><br />

<br />

<br /><br />Well, I'm all 'picture posting' wore out for today.

 

[cobra 3.0]

Re: Another prop question

Brian, real nice pics! Makes me want to go fishing!

 

[markvan]

Re: Another prop question

If you run the risk of hitting rocks I would say stick with an aluminum prop. As far as MINOR dings on the leading edge I usually use some fine grit sand paper on any aluminum that is mushroomed back over the face or bace of the prop. A minor ding (key word minor ding)in the leading edge is not going to cause any significant imbalance on a light small diameter (under 15 inches most props) aluminum prop. <br /><br />15 years in the cooling fan and turbine business, I know that a NEAR PERFECT leading edge is not always a reality once it has been running for a while.

 

[jjboor]

Re: Another prop question

Does it ever end? I just found out that I need to replace my vro pump. I already replaced my starting engine, trim unit. Now I read that my dinged alu prop is damaging my engine! And needs an already scheduled replacement right now!<br /><br />omg and I thought I had a cheap boat. well newsflash: they don't exist!