TOPIC: Link & sync?

It's been suggested that the porpoising I'm experiencing with my Power Cat may be the result of "link & sync" of my merc. Does anyone know what that means, and/or how I would check it?

Thanks!

Frank

It stands for Linkage (throttle-carb, timing) Synchronization, Frank. The Merc manual takes you through it step by step (think it was in the tune-up/maintenance section), but I had to read it numerous times before it finally made it through this tired old brain o'mine!

I don't understand how that could be part of the porpoising, as it's motor tuning. Your Merc sounds like it's running pretty good, although super-tuning is always a plus. I would think the porpoising (minor in your case) would be more related to trim position or weight distribution than tweaking the motor for a few more horses. Just my humble opinion bud. Does it get better/worse with more/less throttle? Have you tried trimming up/down a tad while it's doing it to make it stop?

My motor seems to run just fine Mark. Certainly super-tuning helps every motor, but for instance with my hot rod, I don't worry about it. If I was drag racing, I would be concerned. Likewise with my Power Cat, if I was in regattas or any kind of racing it would make sense, but that is not my intent. The motor runs smooth, does not bog down, hesitate, surge, or do anything like that. It seems to run fine, but wants more trim to get up over 5 grand in rpm.

I've tried about every trim position I can as well as weight distribution at various rpms and cannot drive through it. I run the boat all the time with the motor tucked in, and it's killing both Gail and I because of our backs. It is not any fun at all, and Gail made it known yesterday she's not getting back in it till it's "fixed."

I sent an email to Nauticus last night about their Smart Tabs ( www.nauticusinc.com/smart_tabs.htm ) and am waiting to hear back today. It would be a problem putting them on just because of the design of the hull with drain tubes at the bottom of each sponson. The tabs are supposed to be mounted at the very bottom of the hull, kind of a problem in my case. Folks say they essentially eliminate porpoising. The other idea folks have suggested is a whale tail for the merc.

I don't know enough about this stuff to have much of an opinion. All I can do is hope somebody has an idea. Trim tabs sound good so far, but again, I need to hear from them about questions I have.

Power Cats are supposed to be great in chop, and plane such that they're just riding on the rear sponsons. I don't want much, just to get this figured out!

Frank

Frank I hope this helps! I had a 16' aluminum V hull fishing boat that dolphined very bad. What I did was add weight to the front of the boat and it held the bow down and fixed it. Now the weight thing. I wound up using 2 heavy anchors but theirs lots of options. I started out using solid 1/2 concrete blocks (there cheap)small and heavy but again lots of options for weight.
Good Luck,
Pete

Maybe that's what I should do before changing props Pete is just take some concrete blocks out and play around. Man, I hate adding weight to the boat, but that sounds worth a try.

When I throttle up, the nose comes right up, then settles down pretty quickly, just what a guy would want. The problem is from there, can't trim it out without porpoising.

Frank

What exactly does that boat weigh?
What does the engine weigh?
What is the HP?
20" or 15" leg?

Certainly weight up front will likely solve the problem, but are you using an engine signifigantly larger than the boat was designed for?

My little 12' with a 6HP porpoises badly with one person in the boat. (Tiller control) Add a person up front and it is perfect.

The boat weighs about 300 #s Jim, the motor weighs (I believe) about 260 #s. The motor is a Merc 1000, 20 hp more than the max recommended motor (I think the 800 and 1000 weigh the same). It was a short shaft boat, I made it into a long shaft. The cavitation plate when the motor is vertical is just above the bottom of the middle sponson.

Frank

Frank just rememberd another thing. A friend bought a new boat and had the same problem. After 3 tries the dealer wound up bringing the engine about 1" above the transome where the engine sits on top of the transome. The dealer had to re-mount the engine and used a spacer between the trnsome mount on the engine and the transome. Needless to say my friend was not happy at all about drilling more holes in the transom on his brand new boat!

So 100HP on a 300 lb. boat. That must fly. Maybe the boat needs wings instead.

Is there a spedometer? If so, how fast are you going?
If the weight works up front, which it should, then seriously consider adding a fuel tank (a large one) up front. Then only keep a small 3 gal. in the back for emergencies. You will know fuel is getting low when you start to porpoising again.

After looking at that 9 page thread, you have the battery 2 fuel tanks the engine, all in the back. Then you are running it with two people at the middle of the boat. Is there any weight up front other than fiberglass?

I hope you don't have to remount that engine after all that work.

Got GPS Pete. Going 38 with the motor tucked in!

Power Cat people say weight should be in the back to deal with porpoising. Got a lot of weight back there already, added my wife briefly yesterday, no noticeable difference. I'm gonna go the concrete block route up front I guess.

Frank

Link & sync has nothing to do with the porposing

your CG (center of gravity) is off.

re-distribute weight , engine trim and engine height can solve this issue

Frank, not sure why people always suggest weight on the bow.
When I do get around to building my cat, I'm gonna have built in tanks [and batteries] near the middle, set far outside. [Probably between the front/rear seat area, or under the dash, but not up to the nose.
Unscientifically, of course, I expect it to have good balance that way. You might as well try that out, too.

Other than that, I'd also suggest messing with a different prop. I think its amazing how the way the prop cuts into the water can effect so much of the ride.

I think I'm gonna try sumpin a bit different Jim, and order these babies tonight: www.boatersworld.com/product/MP63527244.htm

Here's the company web site: www.nauticusinc.com/ One of the Power Cat guys recommended them.

For a bit over a hundred bucks, it looks worthwhile to try. I'm gonna have to play around a bit because where they mount is where my drain tubes are, but I believe I can get them on.

I think I have the right prop on (or close), I just can't trim the motor out, and accordingly, can't get my rpms up to where they need to be. Maybe I need a different prop, but until I can get this boat to trim out and plane the way it's supposed to, it does no good to experiment with props. I think anyways...

The trim tabs are about what a new aluminum prop would run, and holes in the transom can always be filled and painted over if they don't do what I need them to do. Everything is an experiment!

Frank

If your willing to spend $ that should work Frank they will affectively change the CG

sounds to me like you need to drop a pitch in your prop to get your rpm up

I have a 19 pitch I can put on Michael, but if I can't get on plane to trim the motor out, thereby gaining more rpm, why play with props? I mean, without being able to trim the motor out, I'll never get a true rpm reading. If nothing was to change, yeah, but I need to get this motor trimmed out. I think if I could I'd be in the mid-5000 rpm's with the 21 pitch I got.

Frank

WoW....I hear these same things for this same problem. Be VERY carful putting loose blocks of anything in your boat....One wrong wave and you feet will get it.I just helped a freind fix this same problem on his g3,the problem is your hull has a rocker,that is the last few inches before your transom, curves up....letting your hull ROCK up and down. 2 easy fixes, a whale tail on the engine will usuly help,but slow you down 1-3 mph, the other is to add some fiberglass to the last few inches and build it up at least 3/8 of an inch beond flat, like an upside down spoiler on a car. please dont put...sand bags - concreat blocks-lead weights in a boat, Use a strait edge and ck the hull for flatness. a qt of resin and a small pac of 3" fiberglass tape should cost 45-60.00 and last as long as the boat. DLOE FIN's work well also and take just minutes to install.....just my opinion.....

Rocker was built into a lot of boats back when, very possible. Lay a 3' straitedge along the bottom to check. Also, how much cup do the blades of your prop have? Cup is needed at the motor height you have. Round ear props also lift the bow with trim, maybe a cleaver blade, which lifts the transom, will be the ticket. Something doesn't seem to add up. 100hp on a 300 pound boat should run faster than 38, especially a tunnel design. I would expect mid 40's with that 21 pitch. Also, some hulls have an inherent speed they just don't like, and another 5mph cures their ills. Raising the motor even 1/2" can also be a miracle. Tuning and tweaking a package like yours is like tuning the hot rod after the motor is done (gears, tires, shocks, etc.) to find the setup that makes it run happy. And remember to test each change before making another. Keep us updated.

frank, gail sounds just like sue. the bouncing hurts her as it does me. the choppier the water the worse it gets. it ran nice and smooth the first 2 years. well i'm trying the cheapest way out. sand bags. if they don't work. i will probably give up. i'm hoping the flat water is the cure. ron

Ponyboy wrote:

WoW....I hear these same things for this same problem. Be VERY carful putting loose blocks of anything in your boat....One wrong wave and you feet will get it.I just helped a freind fix this same problem on his g3,the problem is your hull has a rocker,that is the last few inches before your transom, curves up....letting your hull ROCK up and down. 2 easy fixes, a whale tail on the engine will usuly help,but slow you down 1-3 mph, the other is to add some fiberglass to the last few inches and build it up at least 3/8 of an inch beond flat, like an upside down spoiler on a car. please dont put...sand bags - concreat blocks-lead weights in a boat, Use a strait edge and ck the hull for flatness. a qt of resin and a small pac of 3" fiberglass tape should cost 45-60.00 and last as long as the boat. DLOE FIN's work well also and take just minutes to install.....just my opinion.....

There is NO hook in my hull! I blueprinted it, it is PERFECTLY flat the entire length of the hull, sharp sponson edges, NO HOOK! That is not my problem, or if it is, I have a lot bigger problem than I thought. Motor runs great. trying props right now, results won't be in for a while, at least till I run out of money and patience.

Frank

Double check your hull for a hook! I know you think you dont have one, but 1/8th inch out will mess up your day. Id say most people with porpoise problems can be directly related to a hook.

Ive owned many old boats and the ones that bounced all over had slight hooks to them!

I can plane a kitchen table as long as it is flat without a hook. Take the same table and put a 1/8th inch hook in it and good luck.

My carlson contender has a hook built in for safety. I have to work the hyd trim all the way thru the power application to tame it out. And it dont get smooth until WOT when the air speed supports the bow up.

Also you have added 5 more inches of height to your transom. That extra height gives the motor more leverage to do things the boat. And if the boat is not in perfect running shape those extra 5 inches amplify existing problems.

Conrad

Conrad, I checked the hulls with an aluminum straight edge to make sure they were level when I was rebuilding the hull. I screwed around with them quite a bit to get there. It sits on a flat bed trailer just fine, no rocking at all. (Check out my work: www.powercatboat.com/Group/FA_14t/FA_14t01.html ) I'll re-check it this weekend with the same straight edge. It sure won't be easy to do. Maybe I screwed it up rebuilding it and missed something, but I spent considerable time making sure it was perfectly level.

A Carlson contender is a very different boat than a true tunnel hull. I have three hulls and two clear tunnels, where the Contender tunnel fades back to a single stern hull, much like a tri-hull, at least the ones I've looked at.

The 5" I added to the transom match the 5" taller motor I have. Granted I changed the geometry, but this was not an original thought on my part. Other Power Cat owners (and G3 owners) have done the same with fine results.

I'll keep y'all posted as I proceed through this process.

Frank

That picture, and seeing your video again, shows a hull dilemma. The tunnels are trying to lift the stern, the "flats" of the sponsons and center pod are trying to ride level. I think the hull is fighting itself. Add some mph so the tunnels can take over. Still think your 'Cat is capable of more with a little tinkering. I have a question, tho. Can you take a side picture of the boat sitting still in the water next time you are out?

Hi Frank, I just answered your Switzer question on the J block thread.
Anyways, If you are really sure about the bottom, your prop may be the problem, what are you running? The boat may be lifting when power is applied and then just fall back down as acceleration eases as higher speed is approached because the prop can't hold it up. The boat just ossilates between breaking free and lifting then falling back down. Cupping generally helps, high rake design will help. Choppers have both those features but should be run high on the transom to work.
Older props simply have inferior blade design with little holding ability. If using a Cleaver style they also have little holding ability. This has nothing to do with pitch or rpm.
Some hulls have a certain speed where they ossilate, the Switzer you asked about is nasty between 30 and 45 mph above and below it's fine. Bob Switzer confirmed this is "correct" behavior for this particular design.
I am wondering if the boat is too striaight and you changed the natural ossilation speed? Can you raise the motor up on the transom? Weight is last resort band-aid. Dolefins and stuff bolted to the cav plate will be out of the water at speed unless you motor is way to low on the transom. I'd also think about a possible wedge on the bottom, you can try teporary ones. I've even duct taped stuff on, I run the tape length wise to the boat it just has to be done so the water does not peel the front tape edge off. It's micky mouse but just intended as an experiment to see what effect it has.
Just some random thoughts.
Randy

Kerry wrote:

That picture, and seeing your video again, shows a hull dilemma. The tunnels are trying to lift the stern, the "flats" of the sponsons and center pod are trying to ride level. I think the hull is fighting itself. Add some mph so the tunnels can take over. Still think your 'Cat is capable of more with a little tinkering. I have a question, tho. Can you take a side picture of the boat sitting still in the water next time you are out?

Darn Kerry, just came in, did not bring the camera for my test run, just the gps.

When the boat is sitting still in the water, the nose is up. It looks like it just wants to take off. I'll take a pic next time we go out so you can see how she looks. I think she looks great at rest in the water, and on my trailer, I just need to experiment some.

I think the hull is fighting itself to some degree, but more detail in my response to Randy. He asks some good questions, and I got more answers tonight.

Frank

63g3 wrote:

Hi Frank, I just answered your Switzer question on the J block thread.
Anyways, If you are really sure about the bottom, your prop may be the problem, what are you running? The boat may be lifting when power is applied and then just fall back down as acceleration eases as higher speed is approached because the prop can't hold it up. The boat just ossilates between breaking free and lifting then falling back down. Cupping generally helps, high rake design will help. Choppers have both those features but should be run high on the transom to work.
Older props simply have inferior blade design with little holding ability. If using a Cleaver style they also have little holding ability. This has nothing to do with pitch or rpm.
Some hulls have a certain speed where they ossilate, the Switzer you asked about is nasty between 30 and 45 mph above and below it's fine. Bob Switzer confirmed this is "correct" behavior for this particular design.
I am wondering if the boat is too striaight and you changed the natural ossilation speed? Can you raise the motor up on the transom? Weight is last resort band-aid. Dolefins and stuff bolted to the cav plate will be out of the water at speed unless you motor is way to low on the transom. I'd also think about a possible wedge on the bottom, you can try teporary ones. I've even duct taped stuff on, I run the tape length wise to the boat it just has to be done so the water does not peel the front tape edge off. It's micky mouse but just intended as an experiment to see what effect it has.
Just some random thoughts.
Randy

Randy, I think you've hit the nail on the head buddy (oscillation). Last weekend we were running a 21 pitch prop. Can't trim out, start to porpoise. So I tried a 19 pitch prop Monday night, got weird high rpms, very slow speeds, like 23. Brian Lawson suggested I had not let the prop "bite" before opening it up to WOT, so I wanted to check that. worked late last night, no go. Got out tonight though, and there is no question in my mind what's happening with the 19 pitch two blade. Bottom line is when I try and trim it out to get the nose up and the boat on plane, the nose does NOT go up and the prop ends up spinning air. Can't get the nose up.

Next I'm gonna try a 23 pitch stainless prop my prop guy said he would lend me, and bring down the cupped two blade SS prop Brian Lawson has lent me to see if my prop guy can identify its pitch, maybe try that too. This is probably Saturday stuff.

I blueprinted the hull the way Danny Leger, son of the designer of these boats, Ray Leger, told me to do. I don't think the hull can be too straight, but I may be wrong about that. I can raise the motor, but would rather not. I tried to build the transom so that the motor's cavitation plate when vertical is about an 1" of so above the bottom of the center hull.

What kind of wedge? Where?

Tonight I'm ordering Smart Tabs ( www.nauticusinc.com/ ). One of the Power Cat guys suggested them to me, and they get a lot of great reviews. For essentially the price of another prop, I think it will be a good investment, and may get me by the oscillation problems I'm having.

Thanks for the ideas. Again, I think you're right on target with the problem I'm having here.

Frank

How did the new prop work?
Conrad