hwsiii---Need proping advice

I have a 1994 Evinrude 112 SPL motor on a 1995 Sylvan 16 Pro Select aluminum fishing boat. With 15 gallons of gas, full fishing gear, me, and my 5yo son it is only pulling 4800-5000 rpm at WOT. I usually have one or two adults or one adult and my son, so the boat was not even loaded all the way. From cruising through posts I see this motor with the newer ethanol fuels this motor should be running about 5800. The lower unit was replaced by the previous owner and he said he was experimenting with props and called Sylvan to see what was supposed to come on it. Of coarse I only trust the guy as far as I can throw him and he was bigger than me. It currently has a 13.25x17 aluminum prop on it now. It has a few small nicks in it and I was thinking of going stainless but before I do I want to make sure I get my rpms right. I guess I need a starting point to figure this out. It does have a hydrofoil on it also, should I take it off? After I get it figured out with the aluminum prop, will it change any by getting the same size prop in stainless?

Re: Need proping advice

Re: Need proping advice

I should add that the boat shows on NADA that it has a net weight of 890# and it is 16' long with a beam of 6'7". I will also note that the water was pretty choppy and it was hard to get a good run in before backing off due to someones wake along with the chop from the wind. I would like to get out on a nice calm day to get better data. Also the cav plate is about even with the bottom of the boat and the motor is in the top hole(all the way down). I have a bad feeling this is going to lead to me moving the motor up. I hope to not have to because the boat was just repainted and I hate to mess that all up in the back and have to repaint again.

Re: Need proping advice

Re: Need proping advice

Pro,

You might try reading this for a better understanding of changing props for better performance, and for the major differences between aluminum props and stainless steel.

http://forums.iboats.com/showthread.php?t=369057




H

Re: Need proping advice

Re: Need proping advice

Yep, I went through and read it. I am going to get some better numbers either tomorrow or Wed and go from there. I have a bad feeling I have to move that motor up.

Re: Need proping advice

Re: Need proping advice

Without speed figures its difficult to know where the problem may be.
Moving the motor up is a good thing.You could gain a couple of mph or more.
with an improvement in overall efficiency and performance.If you do it yourself doesn't cost anything.The 17" pitch is certainly in the ball park and a 4" change in pitch (to get about 5,800) seems extreme.
Lose the foil for now (might gain a bunch with this alone)if a prop selection is in order a 4 blade will improve hole shot, and ability to stay on plane with less power.Otherwise something like smart tabs is a better choice than a foil.

Re: Need proping advice

Re: Need proping advice

I will get some more details and data and fill out the sheet will all the needed info. I am not sure why the hydro foil is on there in the first place, it was on there when I bought the boat. I will run it with it on and try to get pics and then see where we are at. Then maybe just taking it off would be a good idea, but if the cav plate is still under water then the motor would still have to come up then, right? It just sucks cuz if I move the motor up then the boat has to go back in my shop for a repaint of the back to hide where the motor was. I guess its worth it to get it tuned for the best fuel economy and speed/power configuration.

Re: Need proping advice

Re: Need proping advice

If the motor is low the foil creates 2 problems extra drag and it could be forcing the nose down dragging more boat through the water and then there is to much motor dragging in the water in the water.

Re: Need proping advice

Re: Need proping advice

Ok, good point. I will take off the foil and see what happens. If I can get the wife to cooperate she can take pics of the motor at WOT so I can post them. I hope they come out with the cav plate above the water like it suppose to be. I will get all the info needed and some pics of different things and post up the results. I hope to hit the water Wed night.

Re: Need proping advice

Re: Need proping advice

Don't worry so much about where the AV plate is while running, different hulls will cause a different look at different speeds. Start by making sure the AV plate is not below the hull when the plate is trimmed to be parallel. How high up you can go will depend largely on the technology built into the prop and how it works with your hull design.

Re: Need proping advice

Re: Need proping advice

Ok I did some running on the lake tonight. It was on the choppy side with 15-20 mile winds on a small 400 acre lake. I managed to get a couple runs in with and against the wind. First here is my info.

1.1995 Sylvan 16 Pro Select aluminum fishing boat
2. 16 feet long, 6'7" beam, Net weight is 890
2a Max horse for boat is 115hp
3. I usually carry myself and one more adult and a child. Sometimes myself and two adults. During this test it was me and my 5yo son. Its a fishing boat so count in all the gear.
4. Fishing boat
5. Not sure if its a deep V, but it is a V. Not sure how to figure deree of rise??
6. 1994 Evinrude 112 SPL
7. 112 hp gear ratio is 2:1
8. Manufacturers WOT is 5500 although some members say it should be 5800 ethanol fuels.
9. The AV plate is even with the bottom of the boat with the motor all the way down. There is a rib that runs down the middle of the bottom of the boat and if you go off the bottom of that its about another inch or so. The rib doesn't go all the way back. The last two feet or so has no rib in the middle.
10. not a bass boat and no pad bottom
11. No trim tabs. Had a hydro foil and I took it off for this test and it showed a lot of improvement. I don't know why it was even on there.
12. Prop is an OE I believe, no name just part number: 763463. It is aluminum 3 blade. It is a 13.25x17.
13. My WOT with wind was 5500 with a GPS speed of 42.1mph. Against the wind I averaged out at 41 mph at 5200 rpms. This was worse the other day with the foil on. I had myself and one other heavy adult and the best rpm was 4800 and didn't check speed.
14. elevation is 935 feet above sea level.
15. Motor runs great(as far as I know). I cleaned carbs, did a decarbon, and adjusted all linkage according to repair manual. Compression is a solid 120 on all 4 cylinders.
16. This prop has not been on long. I bought the boat last fall from a guy that had it less than a year. It has a newer lower unit on it(somebody wiped out the old one). The guy said he messed with different props and some were faster but were doggy with more people in the boat. He said he called Sylvan and they told him this is the prop that was suppose to be on it.
17. No damage to prop other than a few kicks on the ends. Prop is about a year old with low hours on it.
18. I was concerned about my low rpms at 4800. I am a little concerned yet how things will change if its me and two adults in the boat, especially if they are bigger guys. I don't want it to be a total dog, but I don't want to lose any speed if at all possible. I also want to make sure things are right with the aluminum prop because I would like to switch to stainless, but want to get the right one.

Hopefully this is enough info to get a good idea of where I stand with this boat so far. If I can make it better I would like to. I did not get any pics taken and I did not get a look at the AV plate in the water at WOT with just me and my son.

Re: Need proping advice

Re: Need proping advice

Your certainly in the ball park.I think there is more to be had. As I usually say; raise the motor to a point just before ventilation(cavitation) becomes a problem.Especially if your not experiencing any venting now.

Re: Need proping advice

Re: Need proping advice

I kind of thought I was in the ball park as well. Its not as bad as thought it was going to be. Taking off the foil made a noticable difference. I am just concerned its going to fall on its face when I have a couple of adults in the boat rather than my five year old. If I did the math correctly it shows my prop slip somewhere between 2-5%. I think this is one of those scenarios I read about when the efficiency is too high and my prop is holding me back. Hopefully possibly moving my motor will give me the extra performance needed to keep the rpms up. I am waiting for Hwsiii to see what he thinks about the data and if he has ever seen this before. I guess I have to mess up my nice new paint job and will be moving that motor.

Re: Need proping advice

Re: Need proping advice

H will surely have some constructive thoughts.
2-5% slip is unlikely.And if raising the motor works its likely to make the slip appear even lower.Probably one of your variables is wrong.I think 8-10% is good
with about 15% suggesting excessive slip unless a heavy or hard to push boat.
I would guess the hull is a moderate V at most should get up on the water pretty
well.

Re: Need proping advice

Re: Need proping advice

Pro, if you will take the boat out with your normal load and give us your WOT RPM and speed we will know exactly where you stand, and Spike is right, raising the motor usually adds a little more speed.



H

Re: Need proping advice

Re: Need proping advice

H, I will definately do that.

I took the boat out fishing again today with my five year old in the boat and we took a nice long run across the lake. This time I got to play with the trim a little more. My run across the lake and back were real close to the same. I my runs were between 41 and 42mph gps with my fastest being 42.7. The rpms were always right at 4200-4300 tops. I am waiting to get out with another adult to create my "normal load" I assume that my performance is going to get worse yet with more weight?
The other problem I have is if I hit a few good waves or someone elses wake just right the boat will start to porpoise pretty bad and I have to cut it down. Also if I get up on plane and cut down the throttle to cruise slower it wants to porpoise unless the water is real smooth. I have been reading that this is somewhat normal for some hull designs.

Lasty, I noticed the trim seems to not make much difference until it gets right to the top of the trim. Then the rpms finaly come up a little and I gain some speed.

Re: Need proping advice

Re: Need proping advice

You meant 5,300 right NOT 4,300.



H

Re: Need proping advice

Re: Need proping advice

yep meant 5300 not 4300. My rpms always top out at 5200-5300.

Re: Need proping advice

Re: Need proping advice

Pro, I will be waiting.



H

Re: Need proping advice

Re: Need proping advice

Sounds good H. I hope to get out maybe sunday, but not sure being mothers day. Don't want to end up in the doghouse. Plus the next couple days they are talking cold temps and rain. They say their may even be snow flurries. Gotta love Wisconsin weather.

Re: Need proping advice

Re: Need proping advice

LMAO, you can have the snow, I like the heat down here, I just don't need the oil headed this way.



H