Glastron SX175 with Volvo 3.0L Prop Question

jsaghi

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Apr 24, 2018
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I have a 2000 Model Glastron SX175 with Volvo 3.0L/SX Drive which I believe is 1:1.97 ratio. Currently have a decent shape aluminum 3-blade 14.5x19p volvo penta prop that has open vent holes in it (one for each blade). The best numbers I've ever seen at a light load were 38mph (GPS) @ 4600 RPM. This was perfect conditions and me playing with trim until it was back and forth between 37 and 38mph.

The load I am trying to optimize for is 3 adults on board and one adult slalom skiing. With my current prop I get 4400-4500RPM @ 35 mph with that load. I think these numbers are pretty good considering the boat, engine, and age so I'm inclined to believe it's running pretty well. Seems like it is.

The holeshot and top speed are both acceptable, however, I would love to be able to get 1 or 2 more mph without sacrificing hole shot (if it's even possible, that's why I'm here asking for advise)

My research has lead me to believe that since my holeshot is acceptable to us and I want a top speed increase, I should stick with a 3-blade prop. It also seems that my best chance of accomplishing this is switching to a stainless prop.

Since I am 100-200 RPM shy of the 4600 redline with my typical load I believe, through online research, that an 18p stainless 3-blade prop might be my best shot. Does that seem correct?

What do you think my best course of action is? I'm willing to spend $300-400 if this can be accomplished and results in having a good quality stainless prop that will last for years. I'm certainly not set on stainless, that just seems the best bet for my goal.

There doesn't seem to be a huge selection of stainless props in 18p.

Do you guys think I should shop for a 17p, 18p, or 19p?

Do you think it is even possible to get 37mph @ 4600PRM with 3 adults and one skier?

Buying a $300 stainless prop and then having a shop rework it for $200 isn't ideal BUT if the prop I choose isn't quite there, could a good shop tweak it a little if I provide them good data? I have two prop shops that are both 2 hours away in opposite directions. I'd love to try props out but don't want to be making the 4 hour round trip more than once. Is there a good online shop that will ship props to try?

Thanks!
 

Sea Rider

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Welcome to Iboats,

Would that be a 3 adult weight optomization + an adult skier skiing behind at same time. A skier if being heavy will kill the nice 3 adult optomization. Will need to drop at least one less pitch from current one, will increase hole shot to compensate extra skier drag, but max speed will decrease a bit. Can't have the best of both worlds on a single prop at same time.

Happy Boating
 

jsaghi

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Yes, trying to optimize for 3 adults and 1 skier in water. The 4400-4500RPM @ 35 mph numbers are with that load. Not trying to have best of both worlds. I only care about performance with skier in water. Current holeshot is acceptable. Would like 1-2mph higher top end.

This is strictly a ski boat. With current aluminum prop (details in first post) I get 4400-4500RPM @ 35 mph with a skier in water. I'm hoping I can get a more optimized prop and get 4600RPM @ 37mph with same skier in water.

The holeshot with the current prop is acceptable. I’m trying to see if it’s possible to get same acceleration with 1-2mph more top speed by switching to stainless or a better designed prop. Seems like it might be possible with the correct prop. Any recommendations on props that might achieve this?
 
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Sea Rider

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Which is the current pitch engine is running now ? Other important issue to know to get the max out of that engine is to know the exact min-max wot rpm range factory stated for that engine. If hole shot posted data with 3 up and skier behind is bit low on rpm need a less prop pitch to pull wot revs up but not exceed wot rpm for engine not to overrev and rev limiter kicks in.

Thay way will better hole shot, but will lose some top end speed. Don't know if there's a prop that can handle both top worlds at same time while improving top end speed ? Will leave that for the prop experts.

Happy Boating
 

jsaghi

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Apr 24, 2018
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4200-4600 is stated WOT RPM range. Currently has a 19p volvo brand aluminum prop. From researching, it sounds like going from an aluminum to a good stainless prop i might be able to keep similar holeshot but increase top speed by 1-2 mph.

Is that too far-fetched?
 

porscheguy

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Jan 17, 2013
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Top speed and pulling skiers are opposite ends of the spectrum.

I’d recommend the Quicksilver Q3, which is a close duplicate of the mercury Enertia. It’s available in 18P. But honestly, the 3.0 is no speed demon. You’re at the point of diminishing returns. You could knock off one inch of pitch and maybe pick up 1mph and a better hole shot. And you could probably do this with aluminum. Best of all, they’re cheap enough that if it doesn’t provide the desired results, you can try another.
 

jsaghi

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Yeah, I know I'm pretty close to as good as it gets with the 3.0L. Have had the 18 year old boat for 3 months and have skied twice a week since. The performance with the current 19p volvo aluminum prop is acceptable to me but I am the kind of person that can't leave "well enough" alone.

The Q3 is the stainless prop I thought would be the best to try. I was going to do 17p, though. The reason I thought 17p for the stainless prop is because Ive read over and over that stainless will be 200 RPM slower than same pitch aluminum prop. And that one inch down in pitch will be 200RPM difference. Since I'm at 4400-4500 RPM with an aluminum 19p, I assume that a stainless 19p will be 4200-4300, a stainless 18p will be 4400-4500, and a stainless 17p will be 4600-4700RPM. Is that a good decision?

I am also considering trying the quicksilver black diamond 3-blade 15.5x18p aluminum prop. What concerns me about that choice is the diameter is a full inch larger than the diameter of my current 19p. I haven't been able to find much info on how dropping one inch pitch but increasing the diameter by one inch changes things. It will fit on the SX drive. Should I not worry about the diameter?

Do you think I would notice a difference in the Q3 vs black diamond? If not, I'll absolutely choose the aluminum but if the Q3 might be slightly faster with the same holeshot, I'd really be tempted to fork over the money to try.

I've read tons about people praising stainless props and how they got better performance due to the stronger material either not bending as much under load or allowing a more efficient prop design. After reading all those praises I wondered if I could get 1-2 mph tow speed increase by switching to a better prop.
 

jimmbo

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There are no hard and fast rules about pitch changes when going from AL to SS. You are doing an apples to oranges change, and sometimes the pitch increases, other times decreases and other times stays the same. Too many variables. I am very impressed with the Merc Enertia, but it is not the cheapest prop on the market. porscheguy mentioned the Quicksilver Q3, which is similar to the Enertia, but cheaper.
A lot of people buy 17ft - 19ft boats with the 3 liter, only to find they quickly want more speed/pulling power. The options are limited to reducing the load in the boat to only the driver and spotter, optimal propping, and trimming. If you are willing to ski at 30 - 32 mph it will do an adequate job, just don't expect tournament speeds while towing. Most people slalom better at 30 than they do at 36 anyway

When I switched from my VP 21" AL. I had on hand a 20" OMC Raker, It turned out to be perfect. About 3 yrs later I borrowed a 20" Enertia from the Dealer and I liked, so I picked a new one up at cost. There isn't much difference between the RAKER and Enertia, but there is a difference, but not easy to describe.
 
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porscheguy

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You’ll never know what a prop can do until you bolt it on and head for the water.

with that said, your best run of 38mph, at 4600rpm results in 9.5% slip. The only increase in speed you’re going to find is through the reduction of slip. If you increase your top speed by 1mph with all other variables remaining constant, your slip goes down to 7.15%. That’s as good as it gets.but there are no guarantees that your boat can turn the type of prop capable of that slip up to the rpm needed to attain that slip number.

translation. The only way to possibly go faster is by reducing prop slip. This can be reduced by removing weight, reducing drag, or changing to a prop with better grip. Grippy props are the result of aggressive blade shapes with cupping. These are harder to turn. You’re right at the limit with your current prop. A Q3 would be unlikely to provide an improved result.
 

jsaghi

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Thank you very much, guys! I was looking for a more experienced opinion on whether im chasing something that is impossible. May noy be impossible but sounds very unlikely. I will pass on the 500 dollar prop but may get the 15.5x18p aluminum just to try if i find it on sale somewhere.

Also, im not at all unhappy with my current situation. Havent had a boat i could ski behind since i was a kid. It BARELY does what i want it to do with the 3.0 but it does fine and the price was right. Pulls me out of the water and to 35mph. Thats enough to put a smile on my face.
 

Sea Rider

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A 18 pitch prop will have better hole shot than the one currently installed, but should drop some top end speed. Only checkable under a wot run. If wanting faster hole shot and slight top end speed increase, just go skiing with driver and skier, much better if a spotter is not requiered. Less weight will better hole shot and top end speed accordingly.

BTW, the rule of thumb about +,- 200 wot revs going one +,- pitch is something unsure, does not applies to every engine/boat combo as many here have found out. On very heavy boats yes, on medium or light combos way more while playing with just pitches and maintaining same type of prop from previous one.

Happy Boating
 

Scott06

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Had a similar size Sea Ray w a 3.0 for many years. Used a Michigan vortex 4 blade 16" pitch for skiing, 18" 4 blade for general use. The 16" really made it easier to get out of the water skiing, and prop was a little over $100
 

jsaghi

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Scott06, What was your top speed and RPM with the 16p? I exceed my RPM limit easily with a 17p and the top speed isn't high enough to slalom ski.

I just received and installed an 18p enertia. I will go ski some after work today and report back what the top speed and RPM are. I have no clue what to expect because I've never run an enertia before. I am hoping for a top speed of 35mph pulling a slalom and a little more hole shot than my 19p aluminum. We shall see!
 

Scott06

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I never did a gps so I think 34-36 mph, 16" would be at 4700-4800 rpm. Honestly as much as I loved the 3.0, you're getting as much as you can on a 3.0. Wonderful engine for cost of ownership and durability, just isnt fast .

We're not great skiiers and im a big guy so holeshot was my goal. I don't think you can keep slalom holeshot and get more topspeed without more hp. If you drop a ski once up you could try more pitch, but I think you'll be disappointed.

Let us know how the enertia works, certainly your best bet.
 

jsaghi

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The 18p enertia was good but I think I need to play with the pvs plugs. My best prop before the enertia was an aluminum 19p volvo brand that has a 3/8" vent hole at each blade. The 19p prop was 35mph at 4400-4500 rpm with slalom in the water and three adults in the boat.

Last night I got 35mph at 4600 rpm with the 18p enertia. That was not WOT. 4600 is the upper range of my 3.0l. It would push to 4700 or 4800 probably but I didn't do it. The enertia had the solid plugs in and had worse holeshot than the 19p volvo prop. I'm not going to rule the enertia out until I can play with all the different vent plug sizes but so far, my aluminum 19p volvo prop is still my preferred prop.

Being that the 18p enertia could still overrev with a skier in the water. I think the 19p enertia might be the better bet. What scares me is the holeshot on the enertia being worse than my 19p aluminum. I, honestly, would take the slower holeshot of the 19p enertia but some of the skiers (my dad) that come with me don't have the strength to be drug forever, anymore.

I will play with the vent plugs and report back after I get to test each size a couple times. My initial impression is that I should just stick with my 19p vented volvo prop. If I can find a vent plug size that gives better holeshot with the 18p enertia but same 35mph top speed, I might keep the enertia. Solid plugs were too slow holeshot, though.
 

Scott06

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I think what you'll find, and why you need to play with the pvs plugs, when you get a prop with cup, bigger blade area basically better bite it won't allow the engine to spin up in its power band as easily. The three blade aluminum slips more so the engine can spin up rpms more easily. Try the plugs, if you don't have any of the plugs with holes, just pull the solid plugs entirely for a test. That will be max ventilation and aerate the prop so rpms should climb quicker.

I think the 3.0 is good to 4800 rpm, does your Volvo tag say differently? I ran my 3.0 at 4800 no issue so I wouldn't go up in pitch considering your skiing use.
 
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I just sold our 2005 Glastron MX175 (owned from new)- best prop was the Enertia 20". It would do 42mph (gps) and I used that number every spring to test boat condition. That was with full gas and my lard bucket only, at about 1800 ft elevation, but spun Volvo 3L to 4800 rpm.
 

jsaghi

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Apr 24, 2018
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Just updating in case someone in the future is interested in this info.

Have the 18p enertia with medium plugs installed at the moment and am getting very good holeshot. Better than with my cheaper 17p props. The caveat is that I reinstalled a whale's tail to achieve this. It was on the boat when I purchased it and I promptly took it off. I decided to try the whale's tail because the enertia seemed to have much more bow rise than the other props.

I bought a pair of Bennett SLT Tabs but don't have a decent place to install them on this transom so I don't know if they will be better than the whale's tale or not. The whale's tale I have is a real thick plastic one and it is fully in the water at speed. I'm sure it's slowing my top speed down at least a little.

So, with the whale's tail and 18p enertia I get 33 MPH at 4600 RPM with a skier in the water and noticeably better holeshot.

Next will try without the whale's tail to see if I gain a MPH. Then probably try to trade my nearly new 18p enertia for a 19p enertia. Anyone interested? :)
 
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