Outboard throwing water in boat, hydrofoils

gcornelisse

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Jun 11, 2008
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I have a 15' Tide Craft Spitfire bass boat with a 35hp Mercury outboard without power tilt/trim. I have two problems that might be related.

Seems like there is only one perfect hole for the trim pin. If I bring the engine just one hole closer to the boat I get water splashing nearly vertical and back into the boat. What in the world could it be deflecting against that would bring it back forward with such a small change? Could too much roll around the corner from the boat's bottom to transom cause this? Or, is this simply an indication that it should not be trimmed that far forward/down?

I'm seriously considering a hydrofoil to get the boat out of the hole faster. 35hp is just little too underpowered for this boat and it takes way too long to get up on plane. Once it finally gets on plane it actually rides really nice. At this horsepower what hydrofoil would you recommend, and do I need to worry about steering torque? And, if I install one am I going to have more problems with water throwing back into the boat like I mentioned earlier? My outboard's cavitation plate is at or within 1-2 inches of the boat's bottom.

Thanks
 

tcindie

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Re: Outboard throwing water in boat, hydrofoils

Have you considered smart tabs?
 

5150abf

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Re: Outboard throwing water in boat, hydrofoils

Smart tabs or a foil depending on your budget, you might also try raising the motor a hole or two, if your cav plate is 2'' below the bottom of the boat you have room to come up, would help top speed too.

Play around with and find a spot it likes.
 

tashasdaddy

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Re: Outboard throwing water in boat, hydrofoils

it sounds like you have too much foot in the water, the AV plate should be even if not 1 inch above the keel, the AV plate should be in the same plane as the bottom of the boat.

KeeltoAVPlate001.jpg
 

NSBCraig

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Re: Outboard throwing water in boat, hydrofoils

Maybe try some transom shims to get the tilt right (I believe bob's sells them)

Definitely get the height right.
 

gcornelisse

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Re: Outboard throwing water in boat, hydrofoils

I think smart tabs are little more than I'd like to spend even though they're not as expensive as I thought they would be for the size of my boat.

I double checked the distance between the lower edge of the keel and the AV plate. Looks like its about 3/4". I'm not sure how much I can raise the engine. I really, really don't want to drill new holes to re-bolt the outboard's mounting bracket. I just finished replacing the transom. I also don't see any adjustment in the mounting bracket. Its a 1986 Merc Mariner 35hp.

Once the boat is up on plane it seems to ride and handle great. Its the getting on to plane which is a bear. The only reason I was messing with the tilt pin was to see if I could get it up on plane faster/easier.

I've also seen a lot of discussion about moving weight forward. However, I've got about as much forward as is practical. The gas tank and batteries are both up against the back of the driving seats below deck.
 

CATransplant

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Re: Outboard throwing water in boat, hydrofoils

Exactly what is the boat's behavior when you go to full throttle to plane? Does it go bow high, then eventually drop down when it gets to planing speed, or does it just plow water until it reaches a higher speed.

If tilting it in causes water to come up the transom, then that's going to be one hole past what you can run. I'm assuming that you're trimming in to try to bring the bow down earlier.

What pitch prop are you running, and what's the RPM once you reach full speed?

Where is the fuel tank and battery? Where is the rest of the gear stowed and what's on board? Where's your steering position in the boat?

So many questions. But they're going to be the key to getting your boat up on the step faster. I'd skip the fin until you answer the questions and let us suggest some experiments.
 

MadProps

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Re: Outboard throwing water in boat, hydrofoils

I agree , sounds like you motor is too low
 

gcornelisse

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Re: Outboard throwing water in boat, hydrofoils

The bow goes high and plows water until enough speed is reached and it will eventually plane. Once its planing it rides and handles nicely. It doesn't porpoise.

Yes, I only changed the tilt pin to see if I could get it out of the hole faster. Once I saw that the water was spraying back up into the boat I just put the pin back to the position where it eventually planes nicely.

I don't have an RPM gauge attached. I believe the wiring is there for one, but I don't have a gauge to install.

Gas tank and battery are up against the driving seats. The layout is just like any traditional bass boat. Driving seats are mid-boat and driver sits on the right. There isn't much more gear than the tackle boxes and the fishing seats. Most of which is on the floor in front of the steering console.
 

gcornelisse

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Re: Outboard throwing water in boat, hydrofoils

Moving the engine any higher sounds like it will surpass the 1" above the keel that people seem to be recommending? Should I be measuring from the bottom of the keel or the bottom of the boat next to the keel?
 

tashasdaddy

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Re: Outboard throwing water in boat, hydrofoils

boat. for the best ride you want that plate above the bottom and in line with the bottom.
 

gcornelisse

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Re: Outboard throwing water in boat, hydrofoils

I'll post some pictures in a little bit. I'll use a straight edge against the bottom of the boat so the alignment is visible.
 

gcornelisse

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Re: Outboard throwing water in boat, hydrofoils

Trim pin is in hole where it rides nicely once up on plane. Prop is 13P.

Straight edge against bottom of boat

av_plate_1.jpg


Straight edge against bottom edge of keel...roughly. Had to use 3/4" plywood to simulate keel thickness because the rollers are in the way to get the straight edge against the keel.

av_plate_2.jpg
 

tashasdaddy

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Re: Outboard throwing water in boat, hydrofoils

motor needs to be raised, one hole, av plate needs to be where red line is. the way the motor is angled, it is pushing bow up. i would raise the motor, and put a set of Nautilus SX smart tabs on it. not a foil.
 

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gcornelisse

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Re: Outboard throwing water in boat, hydrofoils

I'm not sure how to get the AV plate up to the same level where the red line is now? There simply isn't enough transom to push the mounting bracket up that far. Does this engine just not fit the boat? I know its not original. I'm pretty sure someone threw it on to get it sold.
 

tashasdaddy

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Re: Outboard throwing water in boat, hydrofoils

the motor does not have to sit on top of the transom, it is bolted on. give me a shot of how your motor is actually mounted.
 

tashasdaddy

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Re: Outboard throwing water in boat, hydrofoils

most motors have a series of holes where the red mark is for adjustment, but you used the bottom hole to mount the motor. if you had the holes, it would still mean drilling new holes. so my suggestion now is put a set of SX smart tabs on it to get on planes easier and faster. a foil will cause you more drag, and probably other problems with the way it is set up.
 

gcornelisse

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Re: Outboard throwing water in boat, hydrofoils

Hmm... there is no series of holes on this bracket. I need to do some thinking. I'm already way over budget on this boat. Any thoughts on using a jack plate instead? Thanks for the help.
 

gcornelisse

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Re: Outboard throwing water in boat, hydrofoils

I think I need some clarification.... By "the book", and confirmed by the diagram previously posted, the AV plate should be 1" above the bottom of the keel. Correct? Suggesting that the AV plate should be up around the red line is saying that the AV plate needs to be 4 or more inches above the bottom of the keel. I realize we may be talking in generalizations, but that still seems to be a contradiction to me?

I can probably find enough room to mount the engine an inch higher on the transom. 4+ is a whole new ball game. Why wouldn't I just sell this engine and go find a short shaft model?
 
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