Could these lights be causing my EXCESSIVE prop slip?

[kmagnuss]

Here's the skinny:
1989 Action Craft Bayrunner flats boat, 17'
Weighs about 1200 lbs with motor
2007 Mercury 90 2 stroke carb'd

I've been battling a prop slip problem... to the tune of about 35% or more!
Here's what I run: 23pitch 3 blade Mercury black max, 6000 rpms at 37 mph. Speed checked with gps going both ways.
5500 rpms is the sweet spot here.
I've tried a 19 pitch Solas aluminum 4 blade as well as a 21 pitch Solas aluminum 4 blade... the results are pretty much the same.

Here's what I've tried so far...
Started with the motor on the 4th hole (engine raised 4" above bottom). Motor would blow out at speeds above 20 mph or so.
Dropped the motor 2 holes and it runs pretty good here (it seems). Don't lose grip in turns. If I trim up a couple blips I start go get blow out. But rpms after about 5200 go up without much of an increase in speed.
Changed out my tach (twice) and it seems to be accurate.
With motor at this height the cav plate is right on top of the water... seems to be in a good spot from the pics/vids I've seen.

So with not much else to try I dropped the motor to the last hole today... (all the way down). I'm going to try this out next. At this height the cav plate is about 1.5-2" above the bottom of the hull, and about 1-1.5" below the top of the pocket tunnel. Pocket tunnel is 3.5" high, 5" deep, and 15" wide.

Well today taking these pics I realized that my stupid underwater lights might be causing some turbulence which could be giving me the blowout. So before I take them off (and before my next test with the motor down all the way) I wanted to ask if any of you think they could be the culprit.

Thanks.

-Mag

 

[Home Cookin']

Re: Could these lights be causing my EXCESSIVE prop slip?

I doubt it

 

[glenn property of pam]

Re: Could these lights be causing my EXCESSIVE prop slip?

The lights are not causing any major affect (most bass boats have pump inlet screens in the same area). The fact that the cav plate is above the water and the boat will not increase speed coupled with the fact that it will blow out at with a small amount of trim suggests the motor is to high and as the speed increases the hull raises in the water and you reach a limit of the boat wants to lift but the prop wants to blow out so they meet in the middle at 35% slip.

try the motor where it now at the lowest setting and see what happens. Most of the people who run a prop up high also have a jack plate installed.

 

[Frank Acampora]

Re: Could these lights be causing my EXCESSIVE prop slip?

You need a jackplate with at least 6 inches setback. Engine/prop/ anti-ventilation plate is too close to the transom.

Because the boat never rides flat but even at plane is at an angle to the water, water level will "rise" farther out from the transom. In order to run the engine high, the lower unit must be back in that higher water. Thus: You need more setback

 

[kmagnuss]

Re: Could these lights be causing my EXCESSIVE prop slip?

Jack plate is definitely on my short list of things to buy for the boat... but probably won't happen til next year.

 

[Frank Acampora]

Re: Could these lights be causing my EXCESSIVE prop slip?

Looking again at the photos, the third light that sits near the end and on the top of the tunnel or pocket could be causing turbulence as water hits it. If possible, I would remove that one and see what happens. However, if you want to run the engine high, you still need a jack plate.

 

[jimmbo]

Re: Could these lights be causing my EXCESSIVE prop slip?

How about trying a prop that is designed for running at higher transom mountings. Low performance aluminium designs will give less than optimal performance. Enertia, is a good choice as is LaserII. Fury has potential too.

 

[kmagnuss]

Re: Could these lights be causing my EXCESSIVE prop slip?

Dropped the motor to the lowest setting and it did the same thing. Going to pull the lights off tomorrow and see what happens without em.

 

[kmagnuss]

Re: Could these lights be causing my EXCESSIVE prop slip?

Went out today with the lights off and it didn't change. :facepalm:
Got a look back while around 5,000 rpms and the cav plate was too low.

Not sure what to do at this point. Going to raise the motor back up two spots and see what that does.

 

[kmagnuss]

Re: Could these lights be causing my EXCESSIVE prop slip?

Oh, one other thing... I have a set of Nauticus trim tabs, which I love by the way... but I'm wondering if they might be hurting me some also. Took them off today as well and will test next time out. Going to bring all three props with me also. I'd really like to get out tomorrow but have to wait for the sealant to dry... 4-5 days. Ugh.

 

[hwsiii]

Re: Could these lights be causing my EXCESSIVE prop slip?

Kmagnuss, I received your PM earlier and I need much more information and pictures in order to possibly help with your problem. It has been a long time since I have helped anybody online with prop problems, as it is much harder when you can't actually look at the boat and setup in person, as well as see what is happening when the boat is actually running with the different props, but if you are willing to supply me with the information I need I will try my best to help you.

35% prop slip for a boat like yours is extremely high when it should be about 8% to 12% maximum. From past experience with hulls like yours I would recommend replacing the prop at anything more than 15% slip.

Please feel free to send me your phone number by private message and I will gladly call you.

H

 

[hwsiii]

Re: Could these lights be causing my EXCESSIVE prop slip?

Keith, I am including this information to help you, and possibly other people might find it useful as well, to have a better understanding of how the different prop elements and geometry can affect what any particular prop may have and how that prop affects the boat that is using it.


Progressive Pitch Accelerates Better because it has increasing pitch throughout the length of the blade which helps acceleration and yet produces a Good Top End

Fixed Pitch Good Top End but can have a lower acceleration factor and Hole shot and very narrow speed range

Progressive Rake The most Bow lift available with good speed, great holding power at high speeds and Rough Water and less cavitation and ventilation

Flat Rake Has Great Bow lift and not quite as much holding power or Bow lift as Progressive Rake

0 Rake Best prop for Stern lift and produces the most power, it is usually the best prop for boats that have a tendency to porpoise

Trailing Edge Cup Adds Stern Lift, acceleration and theoretical pitch and reduces ventilation as well as increases speed but lowers RPM

Blade Tips Cup Adds Bow Lift because it increases the rake and usually increases Speed as well as lessens Cavitation and Ventilation

Developed Area Ratio Increase Adds more Dynamic thrust at higher percentages of blade area but usually lowers RPMs because of increased surface area of prop

Mean Width Ratio Average Blade Width of prop divided by diameter, higher usually means better dynamic thrust but lower RPM

Four Blades Less Vibration, better hole shot, better holding power, better Cruise speeds with fuel savings as well as slower minimum planing speeds, usually loses a little top speed but it can increase speed in certain cases when it decreases prop slip

Motor Height Increase Will decrease drag and increase speed, if it is too high it will cause heavy ventilation of the prop if there is not enough cup or rake in the prop. It is the cheapest alternative to buying a new propeller, it can decrease drag and increase speed at no costs to owner, just the time spent to change it.

I am also including a prior white paper of mine that shows what the anti cavitation plate should look like when the height of the motor is right on the transom of the boat, as well as the differences between aluminum and Stainless props. http://forums.iboats.com/prop-questions-topics/changing-props-performance-ss-versus-aluminum-369057.html


H

 

[dan02gt]

Re: Could these lights be causing my EXCESSIVE prop slip?

How about trying a prop that is designed for running at higher transom mountings. Low performance aluminium designs will give less than optimal performance. Enertia, is a good choice as is LaserII. Fury has potential too.

I agree with this. You have the small gear case so your stuck with the Laser II or Trophy Plus (both in small barrel).

2nd loose the "Smart Tabs" to test with. They could be giving you too much stern lift causing props that aren't designed to run high to be running even higher thus inducing slip. You could do this by disconnecting the strut and wiring the tab up and out of the way or set them to their lightest setting. Never mind didn't see the part about you taking them off.

 

[hwsiii]

Re: Could these lights be causing my EXCESSIVE prop slip?

Keith, I do detect a problem with the bottom of the transom right in front of the prop, I have marked the area in Red so you can see it easier. I would appreciate it very much if you would take about 4 pictures, 2 from directly underneath the transom in red and 2 more 90 degrees with the hull from directly behind the area in red. Having the transom bottom in this area with a gouge in it could definitely create a lot of air bubbles, traveling directly back to the prop. It may not actually be as bad as it looks in the picture, so I am not positive, that is why I would like the additional pictures.

http://i369.photobucket.com/albums/oo138/hwsiii3/PossibleproblemmarkedinRed.jpg

The following is a discussion I had with wca_tim ( who is extremely knowledgeable about getting every last little bit out of a boat that runs right at 80 MPH )in 2007

H

Where the bottom of the boat meets the transom and the chines needs to be absolutely a clean 90 degree transition, and most commercially built hulls do not have that, they are slightly rounded, which increases the drag a lot more than most people realize. If you make an absolute clean brake the drag is very much improved. Hull design very much influences the final results, doing the strakes can help, but it is more influenced by the transom first, then the chines in most hulls and lastly the strakes. The reason is because it is more important to have clean transitions where the water leaves the boat than it is where the water just runs down the strakes.

Think of it like a prop, the cup is placed on a prop for one reason only, that is to hold the water better so it reduces slip and the same thing happens on a boat at the transom and the chines. On a boat they are not cupped outward (inward) like a prop is but it still creates that extra drag if it does not have a clean transition. If you decided to do this you would need to grind the gelcoat down and just make a thick epoxy with fillers to create these, you can't use fiberglass tape or any type of cloth for this because they can't make 90 degree corners, they have to be 90 degree corners.

wca_tim

H is dead on about cleaning up the lines on the hull... tight corners on pads, strakes, transom, steps along with blueprinting the last couple of feet of hull (using a straight edge to sand out or fill any deviations from completely flat on the pad and bottom of strakes, etc...).

H

 

[kmagnuss]

Re: Could these lights be causing my EXCESSIVE prop slip?

 

[kmagnuss]

Re: Could these lights be causing my EXCESSIVE prop slip?

Geez my camera phone is awful!
I'll take some better pics with the real camera tomorrow.

 

[Tail_Gunner]

Re: Could these lights be causing my EXCESSIVE prop slip?

hwsiii greetings long time no see.....check my post txp prop..i have a puzzle going on....back to topic

 

[limitout]

Re: Could these lights be causing my EXCESSIVE prop slip?

Geez my camera phone is awful!
I'll take some better pics with the real camera tomorrow.

I think what he is trying to see is if that spot on the bottom is damaged or warn thru the gel coat or is it just a spot where the paint came off and the gel coat is still undamaged and intact

its hard to tell what is what with so many different colored paint its like camo so its very hard to see what we are really seeing

 

[hwsiii]

Re: Could these lights be causing my EXCESSIVE prop slip?

Keith, I would appreciate it if you would take pictures with the (real camera) LOL, just like pictures 1, 2, 4 and 5, but get as close as you can and still have good clean pictures that are in focus.
And you are very right limitout, thank you. I can tell by the Green color on the bottom that the gelcoat is gone by the transom, I just can't tell how chipped and rough it is on the bottom and the transom.

Also Keith, if you have a few minutes before you go to work please give me a call.

H

 

[hwsiii]

Re: Could these lights be causing my EXCESSIVE prop slip?

Hi Frank, it has been awhile , but I do agree with you totally that jackplates are great, but I really prefer the ones that you can actually raise and lower while running the engine as that can be extremely useful when fishing in skinny water, like Keith does.

Hi Gunner, I am going to look at your puzzle right now.

H