A bunch of propping questions (R LXI HH 383)

[thealy]

I know there have been many posts about propping a boat, but I can’t find one specifically about an 05 RLXI with a Hammerhead 383. My current prop is an Acme 3 blade, L (I assume this means Left rotation) 1 1/8 (I assume this is diameter of the shaft) 449 (no clue what his this) 13x12.625 V (not sure what the V means). I don’t really know much about inboard propping. I used to drive a 225 Merc outboard on a 20’ fish and ski and really understood all the concepts very thoroughly but this knowledge just does not transfer to the inboard world. It just seems strange to me that my 225 Merc was able to turn a 24 pitch 4 blade prop with a respectable hole shot and my 400hp inboard has a 12.625 pitch prop that, of course, has a great hole shot but shouldn’t it be able to take larger bytes (larger pitch) and actually give me more hole shot and of course better top end. The engine certainly has no problems turning that 12.625 and I really don’t see much difference if I have two or 10 people in the boat. There is just a bunch of extra power in that engine that I am afraid is going to waste.

Also would anyone recommend going to a 4 blade? Does a stainless prop provide any additional value on an inboard? If you hit gravel on a ramp while loading, would a stainless transfer too much energy to the drive train but also not ding up as easily as a brass prop? Does brand of inboard prop matter. And one last question, my existing Acme need to go in to be rebuilt. I am told that it is a machined prop because there are groves all over it where the milling tool removed material. Once it is rebuilt, I am told that it will be shiny smooth. Since I have always been told not to polish a prop because you want it to stick a little bit to the water, would a smooth service be worse than a machined surface (the Acme site says it should make no difference)?

Thanks

[SCOTTDOMINE]

I know there have been many posts about propping a boat, but I can’t find one specifically about an 05 RLXI with a Hammerhead 383. My current prop is an Acme 3 blade, L (I assume this means Left rotation) 1 1/8 (I assume this is diameter of the shaft) 449 (no clue what his this) 13x12.625 V (not sure what the V means). I don’t really know much about inboard propping. I used to drive a 225 Merc outboard on a 20’ fish and ski and really understood all the concepts very thoroughly but this knowledge just does not transfer to the inboard world. It just seems strange to me that my 225 Merc was able to turn a 24 pitch 4 blade prop with a respectable hole shot and my 400hp inboard has a 12.625 pitch prop that, of course, has a great hole shot but shouldn’t it be able to take larger bytes (larger pitch) and actually give me more hole shot and of course better top end. The engine certainly has no problems turning that 12.625 and I really don’t see much difference if I have two or 10 people in the boat. There is just a bunch of extra power in that engine that I am afraid is going to waste.

Also would anyone recommend going to a 4 blade? Does a stainless prop provide any additional value on an inboard? If you hit gravel on a ramp while loading, would a stainless transfer too much energy to the drive train but also not ding up as easily as a brass prop? Does brand of inboard prop matter. And one last question, my existing Acme need to go in to be rebuilt. I am told that it is a machined prop because there are groves all over it where the milling tool removed material. Once it is rebuilt, I am told that it will be shiny smooth. Since I have always been told not to polish a prop because you want it to stick a little bit to the water, would a smooth service be worse than a machined surface (the Acme site says it should make no difference)?

Thanks

I am no prop expert, but I know the two brands that all of us normally adhere to are Acme and OJ. As for pitches and such, can't help you much there. I do know that I have had a prop repaired 3 times (now a spare) and never noticed any difference in function of the prop. But you are correct, it does come back shiny versus the "milled" look you now have. Also, your prop is not brass, as you stated (I believe that would be way too soft), it is Nickel Bronze Aluminum mix (hence the name NiBrAl). I have no experience w/ SS on my particular boat, but wuold guess that if a SS prop were to hit in the water, it would put an extreme amount of distress on the shaft and tranny of your boat.

[Woodski]

You are correct on your assumptions, L is left hand rotation, 1 1/8" is shaft diameter, 449 is the Acme number for the prop which is a 13' diameter x 12.625 pitch. There is a lot of extra power in a tournament inboard, the major reason for a lack of top speed given a 400 hp engine is the wetted area of the hull. The tournament boat has a hook on the transom and is designed to lift the back and drive the front down so a lot of hull is always in the water and a fixed prop angle. This creates a lot of drag, thus limiting top speed. What you get is great tracking and a great wake for watersports. I don't think you can gain any performance by running a "taller" prop (more pitch) based on the data I am familiar with. These props also come with a fair amount of cup in them, which is like adding pitch so a direct comparision may not be appropriate.

This boat works best with a three blade prop. A four blade will offer a slightly better holeshot (maybe) at a cost in top speed since the prop will be spinning way too quick (4 blades v. 3 blades spinning at 5000 rpm) for best efficiency. The machined props do offer the advantage you mention. The repair on a CNC prop is a hand process so you do lose the CNC machining marks. I personally like a stainless prop, there is less flex using a stainless prop, but it is also not as quiet or smooth since the nibral acts as a damper.

[MOBrian]

You are correct on your assumptions, L is left hand rotation, 1 1/8" is shaft diameter, 449 is the Acme number for the prop which is a 13' diameter x 12.625 pitch. There is a lot of extra power in a tournament inboard, the major reason for a lack of top speed given a 400 hp engine is the wetted area of the hull. The tournament boat has a hook on the transom and is designed to lift the back and drive the front down so a lot of hull is always in the water and a fixed prop angle. This creates a lot of drag, thus limiting top speed. What you get is great tracking and a great wake for watersports. I don't think you can gain any performance by running a "taller" prop (more pitch) based on the data I am familiar with. These props also come with a fair amount of cup in them, which is like adding pitch so a direct comparision may not be appropriate.

This boat works best with a three blade prop. A four blade will offer a slightly better holeshot (maybe) at a cost in top speed since the prop will be spinning way too quick (4 blades v. 3 blades spinning at 5000 rpm) for best efficiency. The machined props do offer the advantage you mention. The repair on a CNC prop is a hand process so you do lose the CNC machining marks. I personally like a stainless prop, there is less flex using a stainless prop, but it is also not as quiet or smooth since the nibral acts as a damper.

You have not taken into consideration of hull design. Your outboard could be trimed for max speed, with only a foot or two in the water. A ski boat is a semi deplacemnt hull, no matter how much power you run you will barely get over 50mph. If you are after top speed a ski boat is not for you.

[VinRLX]

You have not taken into consideration of hull design. Your outboard could be trimed for max speed, with only a foot or two in the water.

It is the type of propulsion more so than the hull design. Because of the fixed angle of the inboard prop shaft, the faster you go, the more the bow goes down.

to the site.

[WakeGirl]

I don't know that I'd be worried about having extra power, but you can do some testing to see if the prop is dialed in for the boat. On the bottom end, it's very subjective. Does it have difficulty pulling a big skier or someone with bad form out? Or do you have to be careful of the old "pull-the-arms-out-of-his-sockets" start? The top end is pretty easy though. At WOT you want to be as close to the rev limiter as possible without hitting it.

I'm going to guess that the 449 is a pretty good match for that boat.

[thealy]

I don't care about the top end hardly at all. It will do 50+ and that in an inboard is fast enough. My question was aimed at holeshot. I am just surprised that a 225hp outboard with a 24pitch can push a boat out of the hole respectably but a 400hp inboard is setup to use a 12-13 pitch prop. Trust me the hole shot on the RLXI with the HH is amazing, but if it can be better, why not go for it. Thanks for all the responses.

Edited February 2, 2008 by thealy

[electricjohn]

The outboard motor has a 2 to 1, or there about, gear reduction, which is why it can turn a 24" prop. I have never seen a 24" prop give good hole shot thought. Outboards used for skiing are usually propped at 19 or less, barefoot boats at 21.

I have yet to find the holeshot limit on my boat. So far 8 skiers (with a boatload of observers) with no problem, and I only have the monsoon. What are you trying to do or what are you looking for? Propping down will help, but you will loose top speed and gas useage will increase.

[doughickey]

Electric has it bang on.

Your Merc likely had a 1.87:1 gear ratio. (Roughly 2:1). That means the crankshaft needed to turn TWICE for every turn of the prop. So, when you had your 200 Merc at 6000 rpm, the prop was only turning 3000 rpm. The effect is like cutting your pitch in half. In your case, half of 24" is 12". Roughly the same as your current prop running through a 1:1 tranny.

You also had trim, and possibly a motor lift. Both let you change the angle of the prop shaft to get the bow out of the water to reduce wetted area. (Drag)

With your Malibu, as has been said, the more power, the more you're driving the front of the boat into the water... increasing wetted surface. (V-drives have a bit of an advantage with more weight aft.) Your prop shaft is at a fixed angle, always driving the rear upwards, and the front downwards.

Want more hole shot. Get a flatter pitch...... but, you run the risk of running past the redline at the top end.

SS ns NiBrAl: Sure, SS is harder. In my opinion, not worth the risk to the rest of your drive-train if you hit something. Let that $350 repairable prop take the hit..... instead of the $1000's of damage you may do to the drive shaft, tranny, etc.

All this from a guy who used to run a 200 Merc with a 21" Hi Five.... then moved to a Malibu RLX with a SS..... which has been upgraded to a NiBrAl.

Edited February 3, 2008 by doughickey

[Woodski]

A couple of items based on your comments. To get more low end or holeshot, you might want to aim more towards the 515 Acme prop. It is much like gearing on a car, so a little less pitch will offer a better holeshot since you will have more torque at a lower boat speed. Also, the Hammerhead is probably not the best choice purely for holeshot. The 383 displacement is great, the cam is slightly more tuned for the upper end of the rpm range. Also, altitude makes a difference on what prop is optimum, looking at your profile it appears you are relaitively close to sea level and in a location that is not really warm and humid, so you don't have to reduce the pitch due to ambient conditions. Bottom line, you certainly have plenty of torque and power to operate the boat. As posted, there is enough torque / power to drag several skiers or barefooters up and out of the water with the setup you mention, a much more difficult task with an outboard.

Not many people have actually tested props with the boat loaded and unloaded. It does actually change which prop ends up being the most efficient at accelerating from rest.

[thealy]

The response about the difference in gear ratios is right on. I had forgotten to account for that. That certainly explains the large difference in outboard and inboard propping. All the other stuff certainly explains the minor differences. But I still can’t help think that actually going up to a bit larger pitch would give me a better hole shot because I do believe this motor has enough extra power to spin that prop very quickly and if the RPM’s are there, a 14 pitch is going to move you further through the water than a 13 pitch. I base this on the fact that the hole shot with one person or 9 is almost identical. Of course if you don’t have the RPM’s a lower pitch is better because it allows the engine to develop maximum RPMs the quickest. I guess I would just have to try it.

Just curious, given that Nautiques use a gearing ratio of I think a 2 - 1, do they need to use a higher pitched prop?

[edwin]

From what I've been told, if you drop the pitch any more that HH will be banging the rev limiter with ease. Why you'd want any more holeshot is beyond me...

[jjackkrash]

The response about the difference in gear ratios is right on. I had forgotten to account for that. That certainly explains the large difference in outboard and inboard propping. All the other stuff certainly explains the minor differences. But I still can’t help think that actually going up to a bit larger pitch would give me a better hole shot because I do believe this motor has enough extra power to spin that prop very quickly and if the RPM’s are there, a 14 pitch is going to move you further through the water than a 13 pitch. I base this on the fact that the hole shot with one person or 9 is almost identical. Of course if you don’t have the RPM’s a lower pitch is better because it allows the engine to develop maximum RPMs the quickest. I guess I would just have to try it.

Just curious, given that Nautiques use a gearing ratio of I think a 2 - 1, do they need to use a higher pitched prop?

Current Nautique DD's gear reductions are 1.23:1. V-drives are 1.48:1.

http://buxtonmarine.com/new_boats.htm

Pretty sure the standard prop on a 1.23:1 Nautique is an Acme 4 blade #422 (12.5 x 15.5).

https://www.skidim.com/products.asp?dept=1131

[Woodski]

Don't forget, the holeshot for a boat is pretty much pushing the boat forward from idle, so the engine has to develop a lot of power from basically 1000 rpm on up. There is little slip compared to a torque converter or tire spin so the holsshot is dependent on low end power.

[VinRLX]

But I still can’t help think that actually going up to a bit larger pitch would give me a better hole shot because I do believe this motor has enough extra power to spin that prop very quickly and if the RPM’s are there, a 14 pitch is going to move you further through the water than a 13 pitch. I base this on the fact that the hole shot with one person or 9 is almost identical.

Going up in pitch will not give you better holeshot. The fact that you have good holeshot with the boat loaded or unloaded is reflective of the pitch that you are currently running.

The prop you choose should take you to the top of your RPM range at WOT with the boat loaded the way you most often use it. If you install a higher pitch prop, your RPM will go down. If it is at the bottom of the RPM range or below, you risk lugging--not good for the motor. What you need is a prop that gives you the best compromise of what you want from it, without hitting the limter or lugging. You ought to be able to go from your 13x12.65 to a 13x13 without difficulty. I think if you went to a 13x14 you'd be at or below the bottom of the WOT RPM range.