Reduce Slip on Aluminum Boat

[spego]

I was just looking for a way to reduce slip on my boat. I have a Spectrum 1804 Aluminum bass boat with a 175 Suzuki motor. The boat does have rivets on the bottom of it and the deck is plywood. I run with light amount of equipment and looking at about 15% slip at WOT with 2 guys. Is that good? Could it be better? I am running a Turbo 2+2 26". Motor is up as high as it can go without braking loose. Shaft is 5 3/4" from V.<br /><br />A basic run down of the equipment I run on board:<br />2 batteries (placed about 1 ft back from the driver/passenger seat...not all the way to the back)<br />5 rods<br />1 tacklebox<br />2 anchors (15lbs a peice)<br />a couple of tools<br />2 lifejackets/2 throwables<br />1/2 of a 15 gal tank (normally)<br /><br />boat weighs 1024 lbs stock.

 

[Capn Mike]

Re: Reduce Slip on Aluminum Boat

15% isn't bad....you probably won't get much better than 12% no matter what you do.<br /><br />First, try lowering your motor a notch. You might have the prop in some turbulance up high.<br /><br />Not familiar with that prop....is it a 4-blade? That's certainly enough HP to use an agressive 4-blade SS cupped prop....but if you fish in junk or shallow water, you might not want a SS prop because of the potential damage to the lower unit. In that case, an aluminum or composite prop would be better.<br /><br />I'd kill for only 15% slip....

 

[spego]

Re: Reduce Slip on Aluminum Boat

Ok I was just wondering. <br /><br />Yeah it is a 4 blade prop SS. The prop is really efficient....seems to be anyway. Plus I have been told the prop itself is one of the better props you can get. <br /><br />I can get about 13% if I am by myself but increases to around 15% if I have a passenger. I was really just wondering if this was normal and all. Always thought I should be getting more than 56mph out of this boat but it has been coming up that the rivets cause the problem. But if 15% isn't bad then it must not be slip problem.

 

[tee-boy]

Re: Reduce Slip on Aluminum Boat

What problems are the rivets giving you? How exactly are rivets causing your prop to slip?

 

[spego]

Re: Reduce Slip on Aluminum Boat

The rivets cause drag when the boat goes across the water at high speeds. I have been told that the drag increases prop slip. I guess the 4+4 picks the bow up high enough that I shouldn't be affected by it. It just kind of all rolls back to the fact I can only get 5000 rpm at WOT. Depending on myself or if there is a passenger....the slip goes from 13-15% (56-58mph). I still look at other setups and think there is something wrong. My setup should break 60. Would poor fuel presure cause the engine not to get up high enough? I never checked compression....if the compression were low would that do it? What other things would be happening if either of these 2 things were wrong?

 

[phatmanmike]

Re: Reduce Slip on Aluminum Boat

if compression were low, you would be getting lower hp numbers. if compression isnt up to snuff, its like having a smaller engine.<br /><br />is your motor on a jack plate? or is it just up that high on the transom, if its on the transom that high, thats bad, you gotta lower it a bit and try it again, but a jack plate would do wonders for your setup, hydrolic, manual or fixed height. any one would do!

 

[walleyehed]

Re: Reduce Slip on Aluminum Boat

12%-18% slip is normal on V-type aluminum hulls with rivets.<br />phatmanmike has a good point with set-back, jackplate or solid....change the CG and you may be able to carry more of the boat above water, increasing efficiency, and lower the slip.<br />The boat will handle much better with at least 6" of set-back as well.

 

[spego]

Re: Reduce Slip on Aluminum Boat

Actually I am running a custom built jack plate that has 5 1/2" of setback. I have the height to the point where if the hydrofoil is taken off it starts to vent and loose speed. So its just about perfect....might be able to drop it down a hair but I just left it there. I know if I go another 1" down (its where I started) I can only get 54 or 55 out of it and it is deep enough to run my 3 blade at that point. At my current height the 3 blade will not bite. So if the slip is normal I guess I am doing about right then. Just thought I should be getting more.

 

[spego]

Re: Reduce Slip on Aluminum Boat

The most weight I have in there is the batteries....2 VERY large Diehard marine batteries. Would moving them to the very back of the boat make a difference in some more bow getting out of the water at speeds? They actually can go back about 2 or 3 feet. They probably weigh about 150 or more together.

 

[phatmanmike]

Re: Reduce Slip on Aluminum Boat

I have the height to the point where if the hydrofoil is taken off it starts to vent and loose speed

dude, you said it right there....<br /><br />take off that foil, they do nothing but scrub speed!!!

 

[JB]

Re: Reduce Slip on Aluminum Boat

Don't agree, PMM.<br /><br />A good hydrofoil, like a SE Sport, properly installed helps low speed planing and time to plane a lot.<br /><br />If the engine is mounted too low they can increase drag at planing speeds, but my experience has been that there is little or no reduction in top speed when the HF is on top of the water.<br /><br />Granted, Smart Tabs do a better job of anything a hydrofoil can do, but saying that hydrofoils do "nothing but scrub speed" is incorrect in my view.

 

[spego]

Re: Reduce Slip on Aluminum Boat

I guess i did not make myself clear though....I am at a height right now that if I take off the foil (I have tested it) I actually loose speed. Thats right.....I gain about 3 mph with it on. The prop is actually so close to the top of the water that the foil prevents it from sucking in air. So when I say its up as far as it can go....it is! lol But that foil helps a TON. JB is right there. Granted the tabs might be the way to "do it right" but this foil kicks a$$ in my opinion.

 

[spego]

Re: Reduce Slip on Aluminum Boat

And yeah it is a SE Sport

 

[ddaigle]

Re: Reduce Slip on Aluminum Boat

Spego, didnt you have the other thread with the pictures of your setup? I may be wrong but from what I can tell your boat doesnt have a pad or flat area at the stern and I think you are trying to get high performance pad bottom speed from an aluminum v hull that is not designed for this. Also, that long shaft motor is causing some problems in the leverage dept. making it difficult to fly your front end for reduced drag. Which in the long run is pointless without a pad bottom hull.

 

[spego]

Re: Reduce Slip on Aluminum Boat

Yeah I did have another posting. I dont know maybe I just dont get it. So a pad is actually a flat bottom on the stern of the boat? I always thought that referred to the actual section the boat rode on when it was planed out. The boat does have a V bottom on it....so in other words it will never actually go fast because of the design of it. Why the hell did they rate it (design it) for a 190hp? That doesn't make any sense to me.<br /><br />As far as the motor....yeah I do believe the CG is being affected by the fact it is up so high. I wasnt sure if that was really helping the setup though being the weight was mostly distributed to the stern.<br /><br />So what I get out of all this....its not designed to do it....the setup isn't the best in the world...and it won't go much faster with the hull design....so deal with it?

 

[spego]

Re: Reduce Slip on Aluminum Boat

Boat Hulls <br /><br />This cleared it up a little for me. Never knew that before. My dad's boat has the design with the pad. Makes sense why his has a 90hp and he can get over 45 out of it.

 

[walleyehed]

Re: Reduce Slip on Aluminum Boat

By JB,<br />

Granted, Smart Tabs do a better job of anything a hydrofoil can do, but saying that hydrofoils do "nothing but scrub speed" is incorrect in my view.<br />

It is very true that foils can, in many cases, increase speed....even when they are out of the water on plane, as they re-direct thrust AND help reduce ventilation.<br />Foils can reduce speed if incorrectly installed, no doubt, but usually this is operator error as far as understanding the purpose of the foil being 2-fold.<br /><br />JB's "view" is fact.

 

[walleyehed]

Re: Reduce Slip on Aluminum Boat

spego, you might try a set of 2" transom wedges for a bit more set-back.

 

[spego]

Re: Reduce Slip on Aluminum Boat

What about moving the batteries back another 3 ft? That extra weight in the back would that affect how it runs in the water at all?<br /><br />Got a good deal on a 13 3/4 x 24 Turbo on Ebay....100 bucks. I think I might run that to get my R's up to 5400 or so too. The range is 5000-5600 and it runs 5000 with the 26" Turbo now. Have to see how it runs with the new one next spring.

 

[Jdeagro]

Re: Reduce Slip on Aluminum Boat

Hi Guy's<br /><br />Just noticed this thread.<br /><br />Let me stick my 2 cents in just to clarify a few things. When comparing Hydrofoils to Trim Tabs (Smart Tabs) and the performance results, you need to identify your expectations. Hydrofoils will never give you all of the benefits that trim tabs will. They will give you some assitance to getting on plane ( in most cases), they may even reduce the porpoising. Depending on the hull design, they may or may not help keep the boat "hooked up" in turns, but most V hulls will likely lean harder and nose dive in turns unless you back off the throttle.<br /><br />As someone said, motor height is important to their performance, therefor the simple installation becomes a bit more complicated.<br /><br />I may be biased, but trim tabs (Smart Tabs) will give you far more in all areas of performance. They minimize bow rise to near nothing at any speed, make the boat plane at much lower speeds, improve the ride and handling ( through waves and truns), eliminate porpoising, and increase top speed. The top speed is a function of adjusting the trim tab pressure which involves a simple position adjustment on the plate bracket. It takes only a few minutes if required. And, because they are always active (like the suspension system on youtr car) the overall efficiency of the boat will result in better fuel economy. That has been documented by Trailer Boats Magazine as well as our own tests.<br /><br />It is a matter of what your your expectations are.