Dhadley - My motor and my prop slip more info

[TwoBallScrewBall]

Hey DH,<br /><br />Thanks again for the help last fall when I bought the 'new' boat. You had mentioned a week or two ago that my RPM/Speed numbers seemed off. I did the math and you're right. <br /><br />I remembered when I first got the boat I got 43mph out of it. My problem was the holeshot, it was horrible. So we chatted and I ended up raising the motor up all the way which greatly improved the holeshot. However I never again got above 38Mph. <br /><br />So over the past couple weeks I've been playing around. Here's what I've found. <br /><br />Holes:<br />1 1<br />2 2<br />3 3<br />4 4<br /><br />14.5X19P Stainless OMC prop. <br /><br />Motor at top height (4 out of 4) - Decent holeshot, top end 38mph, at anywhere from 5200-6000 depending on trim (little or no change in speed with RPM with trim)<br /><br />Motor at Next to Bottom height (3 out of 4) - Horrible holeshot, need to really play with the trim to get it to bounce up on plane, or use trim tabs, even with only 2 people on board. Top end is 43mph on gps, at 5400R. (this was the stock setup)<br /><br />I didn't notice it until I moved the engine back down, but at the top hole, I was getting a lot of slip/ventilation in turns. The boat feels a whole lot more 'solid' or 'footed' with the engine back down. <br /><br />I am going to stick with the current setup, because it gives me a nice 30-32mph cruise at or just below 4000R (as opposed to 27-28mph at the same RPM with the engine up higher). I am considering a modest hydrofoil to see if I can get on plane easier. <br /><br />Motor trim to get on plane is weird. If I start out with the motor trimmed all the way down, the engine hits 3800R and will stay there, nose up, forever. <br /><br />If I go 1/4 up on the trim guage, just about the same thing happens. <br /><br />If I start out there (1/4 up) and when speed maxes out there (but not yet on plane) trim up to 1/2 or a little more, it will dro pdown on plane. <br /><br />If I start out at 1/2 up it planes out but takes forever. And a day.<br /><br />So, what are your thoughts?

 

[Dhadley]

Re: Dhadley - My motor and my prop slip more info

The deal on the height sounds about right. That would make sense that its now at the right height for the existing prop but the numbers are still funny. Youre at about 18% slip. Are you sure the prop is a 19 and not a 17?<br /><br />Now whats really wierd is that the trim is having about the opposite effect that it should have. Nose high and trimming up drops it on plane.

 

[Dhadley]

Re: Dhadley - My motor and my prop slip more info

Forgive me if we've covered this before but are we sure the motor is healthy and timed right?

 

[TwoBallScrewBall]

Re: Dhadley - My motor and my prop slip more info

DH, thank you again for always answering my posts!<br /><br />I compression checked the motor before storage last winter, at or close to 100 in all 6 holes. No more than an 8psi difference between highest and lowest (spread was 102-95 if I remember right).<br /><br />I have never checked the timing. Maybe I'll do that this week some time, or next time I head out. I'm in a class in NYC all week and it's a 6 hour round trip commute so I don't have much free time but I will check it the first chance I get. I have never checked the timing on this thing. It needs to be checked at idle and at full advance, right? Boat is in the water tied to the dock, how high should I rev it (in neutral I suppose) for the full advance check? I have my seloc at home and will double check the exact specs before I do it. <br /><br />Checked last week, the prop is definitely no doubt about it an OMC SST 14.5X19. Does not look like it was ever worked or damaged.

 

[Dhadley]

Re: Dhadley - My motor and my prop slip more info

I dont worry too much about the timing at idle. A lot depends on backpressure so it can be different from boat to boat. As long as it idles in the water at 600-700 in gear (the lower the better).<br /><br />You do need to check the timing with a load at or close to 5000. I prefer to leave the boat on the trailer and just back it down the ramp far enough to get water and keep a load on the prop. Ive seen cleats fly off trying to do it tied to a dock without a test wheel.

 

[byordy]

Re: Dhadley - My motor and my prop slip more info

Steve,<br />I'm a long way from an expert, but let me give you some numbers for comparison.<br />My boat is a 1972 21' Dolphin Products closed bow "runabout". Hull is straight, some residual marine growth on the bottom. Motor is a '79 175 HP Evinrude, which was recently repaired, but not overhauled (rings in the bottom two cylinders, long story).<br />Prop is an aluminum OMC, not sure of the pitch, somewhat dinged up. Anti-cavitation plate is roughly even with the botom of the hull.<br />With the trim in the boat comes up on plane with minimal bow rise in the mid 20 mph range. It doesn't "dig a hole", it just rises up on top. I don't off hand know the WOT speed or RPM, but I have seen 37 GPS at about 4500 RPM trimmed out, for a short period. The boat is not trim sensitive and trim only changes the speed and RPM, a modest, but noticeable, amount. When trimmed out there is more bow rise, but the boat still comes right out of the water. I'm still breaking in the bottom two cylinders so I haven't tried WOT yet.<br />Your boat is certainly much heavier than mine, but still should (I think) perform much better than it does. Are you sure you don't have a hull problem; water or perhaps a hook? <br />Bill...

 

[TwoBallScrewBall]

Re: Dhadley - My motor and my prop slip more info

From what little I have gathered from a couple other owners I've spoken to with this boat, 43mph (which by the way was with 2 people and a full 100 gallon gas tank) is great for top end. Wellcraft's literature said that it will do 49mph at 6000Rpm. That's brand new, optimal conditions, unknown load (probably not full gas tank, poles, tackle boxes, electronics, 1/2 full holding tank, bottom paint, etc, etc). So top end I'm happy with. <br /><br />It's just climbing out of the hole that I need to work on. It might just be something I'm doing wrong. Hull is not hooked, I spent a lot of time under it this pring and did stick a straight edge against it at one point just because I felt like it. Don't think it has water retention because it sits in the water right where other identical models I've seen do. No leaning. Nothing else funny going on. It is a heavy boat, no way around that. I can keep it on plane down to 16 mph or so with the trim tabs down, and about 20mph with no tabs. It's just getting there that's the problem. <br /><br />Thanks,

 

[byordy]

Re: Dhadley - My motor and my prop slip more info

Sounds like you have carefully checked everything out. From the description your boat is indeed much heavier than mine. DHadley will have the answer I'm sure. If you're getting the proper RPM at WOT & the motor is making the correct power & is setup properly, perhaps venting the prop or one of the "varible pitch" props might help.<br />Have you considered having the motor dyno checked to confirm that it's healthy?<br />Good Luck!<br />Bill...

 

[TwoBallScrewBall]

Re: Dhadley - My motor and my prop slip more info

Last fall I went ahead and vented the prop, I might enlarge them a bit but I don't want to overdo it. I think they're 1/4" or 5/16" right now. I get 3800R from a dead stop at WOT right now. Did not consider a dyno, I have had the heads off and the cylinders are clean, the compression is good, I just need to check the timing but I think it's more of a trim/prop issue than an engine performance issue. <br /><br />I used an aluminum 15X17 and that holeshot is great but I don't like the loss of cruise MPH.

 

[KCLOST]

Re: Dhadley - My motor and my prop slip more info

Did you vent the prop properly? Was there any change?

 

[TwoBallScrewBall]

Re: Dhadley - My motor and my prop slip more info

Here's the thing. <br /><br />Yes I vented the prop corretly, have done it before. It did help, but when I did it, the engine was higher on the transom. Holeshot did improve. I had 3/8" holes on my last boat, with the same size prop (but an I/O). I might try that, upping these to 3/8". Now that I have moved back down to the stock motor height, I honestly don't know if there is much of a difference, but I am guessing there has to be. <br /><br />I need a jackplate, so I can start out with the motor high up for holeshot then move it down at speed for efficiency. <br /><br />I have off tomorrow. I think tonight I will remove the prop and drill the vent holes out. Worst case, if it vents too much, I will swap in my aluminum 15X17 for the day of fishing then fill the holes on the 14.5X19 later.

 

[Dhadley]

Re: Dhadley - My motor and my prop slip more info

What I keep thinking about is everything youre saying is working backwards from what it should be. You say if you trim all the way in it will never get on plane. If you trim out it will. With the motor too high for normal running it gets on plane better. Lowering it stopped it from getting on plane in a reasonable fashion. <br /><br />A really strange situation....

 

[TwoBallScrewBall]

Re: Dhadley - My motor and my prop slip more info

Yes I agree. <br /><br />I never waited more than 30 seconds or so, but with the trim down all the way it just sits there. If while it's struggling, I trim up to about 1/2 trim, as I'm trimming up it will hop on plane. Every time. Seems it likes the movement of trim more than the actual trim position. <br /><br />Yes the motor at the high hole, while venting in turns and slipping too much at WOT, planes out great. <br /><br />No I'm not crazy. OK I may be crazy, but I'm not misreporting the facts here. <br /><br />Tomorrow is going to be a test day. I am going to:<br /><br />1. Enlarge vent holes to 3/8" on 19P SST. <br />2. Try out Aluminum 15X17 at the lower motor position (maybe I'll like it?)<br />3. Try planing from a dead stop at various trim positions, without adjusting trim while attempting to plane. <br /><br />I'll report back with results. <br /><br />Maybe the boat is actually a manifested poltergiest?

 

[TwoBallScrewBall]

Re: Dhadley - My motor and my prop slip more info

Just had a thought (It happens once in a while).<br /><br />I think maybe in theory I figured out the "trim down won't plane" paradox. <br /><br />Perhaps all I need are larger vents. My theory being that at full down trim, the prop is too low to get adequate RPM (and therefore engine HP) but once I trim up, the prop picks up RPM in the shallower water and whala, plane happens. Bigger vents might buy me the extra RPM I need.<br /><br />Whaddya think about that?

 

[byordy]

Re: Dhadley - My motor and my prop slip more info

Here's a thought and a question for DHadley. Did you say that the motor revs to 3800 and will not turn any faster until you "fiddle" with the trim, and then revs on up into the normal range? If so (big if) perhaps there is a midrange transition issue and the motor is down on midrange power. Possibily the mid range "link & sync" is out of adjustment and if so the high speed adjustment should be off as well. Might be worth a look to check the "link & sync" and WOT timing.<br />DHadley?<br /><br />Bill...

 

[ddaigle]

Re: Dhadley - My motor and my prop slip more info

One of your posts mentioned trim tabs. Do you have them, are they power operated and what are you doing with them during takeoff?

 

[TwoBallScrewBall]

Re: Dhadley - My motor and my prop slip more info

I have tabs. Bennet Hydraulic. I use them a lot to trim in the wind, to keep the nose down in a chop, etc. <br /><br />With the tabs down, the boat comes up on plane well. With just me or just me and the wife in the boat, I don't think I should need to drop them to get on plane. I didn't need them when the engine was 2" up on the transom. Worst case, I'll relent and use them all the time. <br /><br />Maybe I'll do a link and sync tomorrow too. If time and weather allows.

 

[ddaigle]

Re: Dhadley - My motor and my prop slip more info

I may be wrong but I thought that was a major purpose of trim tabs-to get on plane faster and easier. If you got em use em. I think this will help a lot. I believe you dont have enough low end power to spin the 19 prop to get out of the hole without the tabs. As you stated when the motor was 2 inches higher you were ventilating the prop enough to spin your motor up into the power band.

 

[TwoBallScrewBall]

Re: Dhadley - My motor and my prop slip more info

Got some new data today. A little skewed since I was about 200 pounds lighter today (running solo) but...<br /><br />I put on the aluminum 3 blade 15X17. Last fall I was only able to get about 34mph from it, when I lifted the motor.<br /><br />With the motor where it is now, the 15X17 produced 39-40mph on the GPS at 5700R. Holeshot was really good, from no wake speed to plane in about 3 to 4 seconds. At 4000R, where the stainless had ma around 29-30, I am now at about 26mph. If I bump it up to 4400 or so I get around 30mph. I like this prop and am going to use it for a while to see how it performs with more of a load. If it seems to do the trick, I'll see if I can get my hands on a similar stainless one to see what that does. <br /><br />Latest in the saga!