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Help with 18' Cat Craft catamaran

Old 04-04-2021, 05:09 PM
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Default Help with 18' Cat Craft catamaran

Hello,
I'm wondering if I might be able to get some advice. I recently purchased an 03 18' Cat Craft (very similar hull to the later Caracal) with a 115 Suzuki with a Power Tech, 4 blade 19 pitch SS prop. The previous owner mounted it on hydraulic jack plate with a spacer totaling 12" set-back and installed trim tabs with trolling motors. I find that the boat struggles to get on plane quickly, suffers from some ventilation while accelerating, sometimes porpoises, and will easily rev over 6000 rpm at full throttle. I installed a permatrim which reduced the ventilation and does help the plane, but it's still not where I think it should be. I'm wondering if a different pitch prop would help, or maybe if the large setback on the jack plate is causing excess ventilation and causing the prop to slip? I've played around with jack plate height, trim, etc without much luck. The trim tabs do help bring the bow down and get up on plane, but they add a lot of drag and I don't think they should be necessary on a boat this size. Right now I'm thinking that I might need to remove the jack plate, or at least the spacer, to bring the engine closer to the boat and also remove the trim tabs to reduce the weight in the rear before I try different props. Does anyone have any experience, ideas, or insight they can share? Thanks in advance.
Old 04-04-2021, 05:35 PM
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"Dirty" water is directed back from the sponsons towards the prop, common problem with smaller cats, drop down one hole, if it still revs over 6000, increase pitch an inch or two, stay with 4 blade for sure, keep permatrim also....
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Old 04-04-2021, 08:19 PM
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I like Micks advice.

But if you already have a Jack plate that can always come up, you might want to drop 2 holes on the motor mount.

And if the hull will trim the nose down with the trim tabs up and the Permatrim down, I would lose the tabs. The 4 blade prop will want to lift the stern pushing the bow down so it sounds like trim down is covered.

But if she runs bow light and trim down is a problem, take off the spacer and leave the tabs. Small boats love trim tabs as long as their angle is not excessive acting like a brake.

You want to change one thing at a time.
Old 04-05-2021, 05:20 AM
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Don't run it like a v hull. Accelerate to the point of cavitation and then pull back the throttle slightly until prop bit occurs and then throttle back up. I have a Livingston 19' catamaran and it took me a few tries to get the hang of running it properly.
Old 04-05-2021, 06:27 PM
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Originally Posted by Bullshipper View Post
I like Micks advice.

But if you already have a Jack plate that can always come up, you might want to drop 2 holes on the motor mount.

And if the hull will trim the nose down with the trim tabs up and the Permatrim down, I would lose the tabs. The 4 blade prop will want to lift the stern pushing the bow down so it sounds like trim down is covered.

But if she runs bow light and trim down is a problem, take off the spacer and leave the tabs. Small boats love trim tabs as long as their angle is not excessive acting like a brake.

You want to change one thing at a time.
Thanks for the input. I'll definitely change one thing at a time as I go forward.

I actually have difficulty getting the bow down without using the trim tabs, hence my suspicion that I have too much weight on the stern. I'm not sure how much the trim tabs with trolling motors weigh, but I bet that they, along with the jack plate and spacer weigh close to 100 lbs. I've read that these small cats are weight sensitive hence my initial focus there. I'll probably start by removing the space and then if that doesn't work, I'll swap out the trolling motor trim tabs for some normal ones.

I don't think that I want to drop the motor any lower on the jack plate. Right now if I lower it all the way and try to take off I get a large amount of water coming over the transom. Based upon my research, I think that's indicative of an engine that is set too low, although I suppose it could also be due to the jack plate itself.

I tried to attach some photos showing the current setup, but it looks like I don't have enough posts yet.
Old 04-05-2021, 06:28 PM
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Originally Posted by JSR View Post
Don't run it like a v hull. Accelerate to the point of cavitation and then pull back the throttle slightly until prop bit occurs and then throttle back up. I have a Livingston 19' catamaran and it took me a few tries to get the hang of running it properly.
Thanks, I can see how that would help. These cats definitely have a learning curve, but I love the way it handles chop.
Old 04-05-2021, 06:35 PM
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It looks like I can post photos now. Here are a few pictures that show the current setup.





Old 04-05-2021, 07:40 PM
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I see a few things that I would question right off the bat.

Trim Tabs
They are very small and are also mounted wrong. They will ever work right as installed.
They need to be moved out all the way to port and starboard so that outer edges of the tabs meet the vertical outer walls, and they need angled so that they are parallel to the bottoms of the sponsons, slanting to match the deadrise of the sponson bottoms. The bottom of the tabs should 1/4-3/8" above the bottom of the hull, not 3" above and centered. As mounted, they will neverget the nose down without excessive angle and that flap angle will slow you down a LOT. I would also remove those trolling motors as they are creating a lot of drag. The holes in your transoms letting the wire and water come through and also need covers on the holes with 4200, asap to be fixed asap.

https://www.partdeal.com/wiring-elec...ickel%2520Bids

Motor setback
Its really excessive and its acting like a lever to lift you bow. It is also causing a lot of the splash problem you see. If the jack plate can be mounted to the hull, I would do that after fixing the trim tabs. Do you fish real skinny water where you need a jack plate??

Motor Height
We need a picture showing the motor lowered all the way down before commenting on this as the shaft could be too long or short.

Last edited by Bullshipper; 04-05-2021 at 07:50 PM.
Old 04-07-2021, 05:04 AM
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Originally Posted by Bullshipper View Post
I see a few things that I would question right off the bat.

Trim Tabs
They are very small and are also mounted wrong. They will ever work right as installed.
They need to be moved out all the way to port and starboard so that outer edges of the tabs meet the vertical outer walls, and they need angled so that they are parallel to the bottoms of the sponsons, slanting to match the deadrise of the sponson bottoms. The bottom of the tabs should 1/4-3/8" above the bottom of the hull, not 3" above and centered. As mounted, they will neverget the nose down without excessive angle and that flap angle will slow you down a LOT. I would also remove those trolling motors as they are creating a lot of drag. The holes in your transoms letting the wire and water come through and also need covers on the holes with 4200, asap to be fixed asap.

https://www.partdeal.com/wiring-elec...ickel%2520Bids

Motor setback
Its really excessive and its acting like a lever to lift you bow. It is also causing a lot of the splash problem you see. If the jack plate can be mounted to the hull, I would do that after fixing the trim tabs. Do you fish real skinny water where you need a jack plate??

Motor Height
We need a picture showing the motor lowered all the way down before commenting on this as the shaft could be too long or short.
Thanks Bullshipper! I already sealed the hole for the transducer wire and am working on removing the old trim tabs now. They do weigh about 30 lbs each, so if nothing else it will be good to get that weight off the boat. If it turns out that tabs would be helpful on this boat I should be able to reuse the actuator hardware with some standard tabs mounted in the corrrect place.

I plan to finish removing the trim tabs, then I'll test drive the boat before removing the spacer so I can what each change does. I'll also take a picture of the motor height next time I'm there.
Old 04-07-2021, 05:15 AM
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My FIL had what i think is the newer "Caracal" version of this hull (correct me if I'm wrong bullshipper) with a 140 Suzuki and it did ok with just a 4 blade prop upgrade. It was not perfect but it didn't have the perma-trim or tabs on it either. Good riding boat for its size though and was easy upkeep with the skiff like rolled gunnels and splatter paint interior.
Old 04-07-2021, 06:59 AM
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Ok.

I believe the spacer is negating the lift at the stern from your 4 blade prop, but try one thing at a time like we said.

Don't throw the trim tabs away.
Old 04-07-2021, 02:09 PM
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Originally Posted by Shooterschmidty View Post
Hello,
I'm wondering if I might be able to get some advice. I recently purchased an 03 18' Cat Craft (very similar hull to the later Caracal) with a 115 Suzuki with a Power Tech, 4 blade 19 pitch SS prop. The previous owner mounted it on hydraulic jack plate with a spacer totaling 12" set-back and installed trim tabs with trolling motors. I find that the boat struggles to get on plane quickly, suffers from some ventilation while accelerating, sometimes porpoises, and will easily rev over 6000 rpm at full throttle. I installed a permatrim which reduced the ventilation and does help the plane, but it's still not where I think it should be. I'm wondering if a different pitch prop would help, or maybe if the large setback on the jack plate is causing excess ventilation and causing the prop to slip? I've played around with jack plate height, trim, etc without much luck. The trim tabs do help bring the bow down and get up on plane, but they add a lot of drag and I don't think they should be necessary on a boat this size. Right now I'm thinking that I might need to remove the jack plate, or at least the spacer, to bring the engine closer to the boat and also remove the trim tabs to reduce the weight in the rear before I try different props. Does anyone have any experience, ideas, or insight they can share? Thanks in advance.
Here is what I remember about your 18' Cat Craft. It was manufactured by C-Hawk boat in NC. I believe their 18' cat was patterned after Angler Boats 19' cat (made in Miami), which like your 18' Cat Craft was not a popular hull due problems caused by the 3rd sponson in the tunnel, & both cats were only manufactured for a couple of years due to owner rejection because of problems like you are experiencing.

That 3rd sponson like your Cat Craft has below your engine, sticks down like a sore thumb and prevents clean water from getting to your prop <- and that is crux of your problem. Did you ever wonder why the previous owner added a hugh 12" jackplate to that little boat? Answer = to try to get his prop down far enough to reach and get a grip in clean water, and that jackplate upsets the entire balance of the boat. You can continue to do as the previous owner did with band aids - like messing with your trim tabs, the Permatrim, or whatever - none of which will be much help. I've been through this before with a 19' Angler cat and what that hull needed was to remove the 3rd/middle sponson so the prop could get clean water, and I don't know how feasible that would be.
Old 04-07-2021, 05:13 PM
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Originally Posted by Bullshipper View Post
Motor Height
We need a picture showing the motor lowered all the way down before commenting on this as the shaft could be too long or short.
I took a couple of photos to illustrate the engine height. The first is with the jack plate lowered all the way down and the second is with it raised about 1.5" from there, which seems to give me the best cruise performance. From what I've read, the permatrim should be approximately parallel with the bottom of the third sponson.

I haven't measured precisely, but it looks like even with the jack plate lowered all the way, the engine is still an inch or two higher than it would be if it was attached directly to the transom. I don't fish super skinny water, so it might be best to just ditch the jackplate altogether.
​​​​​

All the way down.

Best cruise performance.
Old 04-07-2021, 08:08 PM
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The motor looks high to me in both pics. Is it a 20 or 25" long shaft?

With all that weight sitting so far back behind the transom its no wonder that the bow wants to lift and I imagine it also make the motor sit low to the water with the hull tilting up, making anyone nervous about lowering it more.

If its a 20" losing the bracket and mounting it lower may be your only option, and there is the option of also adding 5 degree wedges to make the motor tuck in more, and they are like $50.But I doubt that they will work with the spacers and jack plate.

Will the steering clear the transom with the spacers removed then the motor tilts up?

Last edited by Bullshipper; 04-07-2021 at 09:10 PM.
Old 04-08-2021, 06:51 PM
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Originally Posted by Bullshipper View Post
The motor looks high to me in both pics. Is it a 20 or 25" long shaft?

With all that weight sitting so far back behind the transom its no wonder that the bow wants to lift and I imagine it also make the motor sit low to the water with the hull tilting up, making anyone nervous about lowering it more.

If its a 20" losing the bracket and mounting it lower may be your only option, and there is the option of also adding 5 degree wedges to make the motor tuck in more, and they are like $50.But I doubt that they will work with the spacers and jack plate.

Will the steering clear the transom with the spacers removed then the motor tilts up?
I checked tonight and I'm pretty sure that is a 20" shaft. Losing the jack plate entirely would drop the engine about 3-4"
Old 04-08-2021, 08:40 PM
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I know it is not identical but I just sold a 18ft leader cat.has the same middle toon. If anything mine was a heavier hull then yours. Had it a couple years. Fully restore . Df90a with a Powertech 3 blade 17 p . Your motor looks high . The transducer needs to move farther away from the prop and is to low .I'm sure you get a rooster tale and dirty ff feeds. Your water line looks to be higher then the suppers. can you confirm this? I would lose the jack plate ,tabs,and permatrim. Start fresh. My boat did not like a 4 blade prop . It had a hole shot so good I never needed to trim and was on plane so quick no matter the load or if I was pulling a tube. I tried so many props and I always went back to the powertech 3 blade. If i Remember right wot was around 32-34mph but my bottom end was so ridiculous on holeshot I'm sure I could have given some up for more top end. But I would not have changed a thing.
Old 04-09-2021, 03:46 AM
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Originally Posted by 757saltwater View Post
I know it is not identical but I just sold a 18ft leader cat.has the same middle toon. If anything mine was a heavier hull then yours. Had it a couple years. Fully restore . Df90a with a Powertech 3 blade 17 p . Your motor looks high . The transducer needs to move farther away from the prop and is to low .I'm sure you get a rooster tale and dirty ff feeds. Your water line looks to be higher then the suppers. can you confirm this? I would lose the jack plate ,tabs,and permatrim. Start fresh. My boat did not like a 4 blade prop . It had a holes shot so good I never needed to trim and was on plane so quick no matter the load or if I was pulling a tube. I tried so many props and I always went back to the powertech 3 blade. If i Remember right wot was around 32-34mph but my bottom end was so ridiculous on holeshot I'm sure I could have given some up for more top end. But I would not have changed a thing.
Thanks for the input. The water line is right at about the scuppers. If someone walks to the back of the boat some water will come in. That's what originally made me think that I have a weight problem.

I'm definitely removing the tabs and plan to tackle the jackplate next, although I hope to remove the spacer first for a test before I go all the way.

I don't get a rooster tail, but I'm not sure what you mean by "ff feeds". Can you clarify? What would you suggest for transducer placement?

Thanks again!
Old 04-09-2021, 07:34 AM
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The tunnel height, or top of the tunnel on your cat is very low, so the air being funneled into the tunnel from the bow has no where to escape to as the top of the tunnel at the rear is fully submerged. You therefore will have to have the antiventilation plate, the Permatrim and the prop below below the level of the keels and bubbly water to get cleaner water to the prop. It probably will never be completely clean even if you lower it a lot, but your prop will ventilate less the lower you go. As an example, my cat tunnel is 25" tall for my 25" motors, so even at rest there is always 7-11" of air between the top of the tunnel and the water surface where air can escape up and away before it gets to the lower level of my props. Your tunnel looks to be about 10" high.

Removing the tunnel sponson is not practical structurally and because the tunnel top is so low, that will really not alleviate the air trapped your propeller water either.. Moving the motor closer to that center sponson will however shield the lower unit and reduce a lot of the splash up you are getting.

Because you have air trapped in the tunnel, your transducer is also probably getting bubbly water and the previous owner probably positioned its as low as possible to get a better signal. The profile on your skimmer transducer is as narrow as they come, so I believe that the setback on the lower unit of your motor is causing a lot more splash and the Transducer and untillyou get the bow down, you will not be able to set the transducer perfectly anyways because the stern will raise and the bow drops, so first things first.

I believe that the 4 blade prop is the way to go. The long setback and high positioned prop are what you need to address first to get the boat riding with only a 2-3 degree attack angle using a neutral trim angle on the engine and Permatrim.

So I agree with First Light in that this model will probably never run perfect, but I am sure we can get it riding faster, dryer and smoother than it was when you got it, and no hull is perfect that I have enjoyed either.


Last edited by Bullshipper; 04-09-2021 at 09:03 AM.
Old 04-10-2021, 10:59 AM
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Hey OP. How do you know that 1.5” up is the best cruise performance? Do you have fuel burn number readings? What are you basing that off of? Reason I ask is my Caracal runs most efficiently with the jack plate buried. If anything I could drop my motor down a notch to see if it gets even better. And it appears that mine is mounted lower than yours. I will try to upload a pic of it all the way down.
Old 04-10-2021, 11:01 AM
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All the way down. Sorry about the tilt, just how I keep it on the lift.

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