Prop slippage in a deep-vee-inboard

WHAT PERCENT OF SLIPPAGE IS TO BE EXPECTED WITH A SURFACE DRIVE PROP IN A DEEP-VEE-INBOARD BOAT.

We know a submerged prop in the same boat slips about 20%.

We also know you must run a prop which has more pitch than a submerged prop to get the same speed out of surface drive.

So to get a true speed of your boat you must know PITCH X RPM - SLIPPAGE.

Please no talk of Radar, or GPS thank you.

I would like not to spend 100,s of dollars on props to get the right one.

I use this formula........pitch x rpm divided by 1056 for no slip speed then mustiply by .79 to get actual speed at a 21 percent slip rate on a deep vee surface drive boat.

John

Now the million dollar question is what number do you use for pitch?

Measure the first 20deg from the leading edge with no slip factor.

Just what I have found with logging a few setups.

Dave......Interesting way to measure.

I am editing this message because as I was trying to write from the cell phone earlier today and got frustrated and did not explain as I would have liked.

Terry..........good question. Who in the world really knows. I use my own measurement system and I figure it does not matter so long as my numbers work for me. I use the Steve Much gauge at the pond for reference and make changes in thousandths of an inch usually halfway up the blade at the trailing edge and the tip to get the engine rpm where I want it. I use the radar gun now a days along with a tachometer. That to me is the best solution.

That is not what Mark wants to do so .....

Mark........I suggest you get with Mark Sholund , Andy Brown, or Bob Austin. They are the prop guys and can tell you what you need for your boat without you having to spend a lot of time and money finding the right prop for your boat. The slippage rate on your deep Vee will change dramatically from calm water to rough water. The 21 percent rate I noted earlier is for SAW running with the boat aired out.

mark adams said:

WHAT PERCENT OF SLIPPAGE IS TO BE EXPECTED WITH A SURFACE DRIVE PROP IN A DEEP-VEE-INBOARD BOAT.

We know a submerged prop in the same boat slips about 20%.

We also know you must run a prop which has more pitch than a submerged prop to get the same speed out of surface drive.

So to get a true speed of your boat you must know PITCH X RPM - SLIPPAGE.

Please no talk of Radar, or GPS thank you.

I would like not to spend 100,s of dollars on props to get the right one.

Click to expand...

Mark, Forget about those details.

Ask around for what is the best prop for your set up and then fine tune from there.

Prop slip is a very complex subject that most people have no clue about....not even the guys that think they know.

Andy said it right.

You can take 2 IDENTICAL boats, modify the engines exactly the same, use the same pipe, exactly the same length, 65% nitro out of the same can and one of the boats will be faster or handle better than the other.

I read my props with a Orlic gage at 70% from the hub then 20deg of travle from the leading edge.

I use the leading edge pitch as the mark to base the top speed of the prop.

If the prop is working to its full potential It will reach this speed in the straits based off the RPM and GPS logged on my eagle tree.

This lets me know how the prop is working.

It will tapper off in the corners as the load changes and it slips.

I have not seen the boat go faster than the lead in pitch logging the boat.

This is one tool I use to tune my props.

John Finch said:

Terry..........good question. Who in the world really knows. I use my own measurement system and I figure it does not matter so long as my numbers work for me. I use the Steve Much gauge at the pond for reference and make changes in thousandths of an inch usually halfway up the blade at the trailing edge and the tip to get the engine rpm where I want it. I use the radar gun now a days along with a tachometer. That to me is the best solution.

That is not what Mark wants to do so .....

Click to expand...

Yup, just being a smart ass.

Everyone seems to have different "standards", how someone can quote pitch numbers to someone without saying how they're arrived at I don't know.

Would be better as Andy suggested to say what you're running and go from there...

Here we go I know I'm going to open a can of worms but I see no other way.

I will be running a Muck super Spartan 50 inches long 13 inches wide with a g26 Zenoah with a submerged drive.

I realize everyone is running surface drive I don't want to. No body knows how to prop a submerged drive. I was hoping I could get the prop numbers from a surface drive boat figure out the slippage and reduce the prop size by that rate but if you read the letters above that idea is not working out so you suggested to give all boat information. Here is the information. This will be a oval racing boat.

mark adams said:

Here we go I know I'm going to open a can of worms but I see no other way.

I will be running a Muck super Spartan 50 inches long 13 inches wide with a g26 Zenoah with a submerged drive.

I realize everyone is running surface drive I don't want to. No body knows how to prop a submerged drive. I was hoping I could get the prop numbers from a surface drive boat figure out the slippage and reduce the prop size by that rate but if you read the letters above that idea is not working out so you suggested to give all boat information. Here is the information. This will be a oval racing boat.

Click to expand...

There are a few guys on here that made the transition from subsurface to surface years ago and should have an idea of how much smaller the prop should be compared to the current g26 powered surface drive boats.

My guess would be an X467. If it seems to be a bit too much just reduce the cup a little....or a lot if needed.

I can tell you on a 60 mono A common prop was an Octura 1455. For an OPS 60 if you ran a Rossi 65 you jumped up to almost 3 1/2 inch pitch and the motor ran totally different. Ed Hughy used to put out a Pitch Gauge it gave you prop slippage speed chart I still have one.

What I did was I started with what other guys were using then made changes to the prop pitching up or down, not everybody knows how to do that. I ran a flatbottom drag boat in northern Michigan and owned boats all my life so have an idea of how prop design affects certain boats. Even had a modified huricain 10 merc on a hydro when I was 14 it was really cool

I am also heard that Octura 1465 will make your set up move pretty good I don't know what you guys are running for RPM on Zenoah engines I can't magine exceeding 15 or 16,000 in reality probably closer to 12. 1465's were also common for oval racing on out rigors with a flex shaft you could start your depth about 7/8" to the centerline to the prop shaft and just raise it and 16th inch increments until you think the boat is winding up good moving good. The X series props may provide you a slight performance edge. On a boat like that it doesn't hurt to have a couple props because you might have a rough water prop and calm water prop. I prefer heavier brass flywheels on all my OPS engines is they are better in rough water spinning more pitch

Robert is right on with the 1455 for a submerged prop with a 65 motor. My experience when I went to surface drive with the same boat was an x462 prop. Keep in mind............going surface drive lets the transom settle into the water for good control. A subsurface prop at the speeds the boats are running today will lift the transom out of the water and make it chine walk terribly.

John

Guess you can use these charts as a guide or starting point:

[A] [SIZE=13.5pt]basic guide lines for the different types of hulls:[/SIZE]

[SIZE=10pt]DEEP-VEE - INBOARD - SUBMERGED PROP- 3.5cc - 1337/3, 1640, 1938, X438
DEEP-VEE - INBOARD - SUBMERGED PROP- 7.5cc - X445, X447, X645, X646
DEEP-VEE - INBOARD - SUBMERGED PROP- 11 cc - X447/3, X448, X452, X646/3, X648, X548
DEEP-VEE - INBOARD - SUBMERGED PROP- 15 cc - X455, X455/3, X457, X457/3
DEEP-VEE - INBOARD - SUBMERGED PROP- 22 cc - X460/3, X465, X665, 1465, 1662
DEEP-VEE - INBOARD - SUBMERGED PROP- 25 cc - X460/3, X465, X665, 1465, 1662
DEEP-VEE - INBOARD - SUBMERGED PROP- 30 cc - 1470, 2167/3, X467, X470, X670, 1567[/SIZE]

[SIZE=10pt] [/SIZE]

[SIZE=13.5pt]Prather Suggested Prop Usage Chart[/SIZE]
[SIZE=10pt]Prather Props - [/SIZE][SIZE=10pt]Use the following prop usage chart to match the proper prop to your boat and engine. In many cases more than one prop is recommended. The 1st prop recommended is the smallest followed by one or two larger props. The 1st prop recommended is generally used for low nitro or where high R.P.M. is needed. It's also great for breaking in new motors. The 2nd and 3rd props are for higher nitro fuels (50% to 60%) or where a higher strut height is used. Propellers are supplied 'as cast' and must be balanced before use. [/SIZE][SIZE=10pt]Order Prather props now[/SIZE]