2003 Crestliner Superhawk 1700 - Porpoising

[Dragonsm]

Quick specs on the boat we purchased this spring

Crestliner Superhawk 1700 walk through with a Yamaha F115 (max is 125 for the boat) on the back

Original Prop (Turning Point hustler 13 1/4 x 19 - horrible prop for this combination! was replaced with a Yamaha 13 1/4 x 17 -recommended both by Jay Soderblom and also many web posts...RPM's are now sitting around 6,000 WOT...speed is right around 39-40 - 2 adults & 2 young kids)

Motor is mounted 2nd hole down from top, anti-cavitation plate it lined with the bottom of the keel of the boat.

Zero blowout/slipping when turning (regardless of how sharp of a turn)

When up on plane, I'll play with the trim of the motor for a more optimal/comfortable ride for the family. Much past a little trim (maybe 1/4 trim at most on the gauge), It starts to porpoise. (not sure how to explain, but the transition from the slow trim up to the "fast" trim up is shown as completely trimmed up on my gauge)

The change in prop helped tremendously, and I've played around with weight distribution a bit-moving people around, anchors..etc. (3 batteries in the boat, 1 up front, 1 at the console, 1 in back) Limited time on calm water and a wife that isn't comfortable driving the boat yet hasn't allowed me to hang over the back while on plane to check out the anti-cavitation plate and see where that is riding.

My next thoughts are to maybe try and raise the motor up another hole to have it inline with the bottom of the V hull (about an inch up) and the other recommendation was to add a little hook into the transom.

If this was my father's boat, he'd be happy with it and leave it.....My family and I love the boat, but I tend to like to "tinker" a bit more as I know it could be dialed in a bit more, and the classic Band-Aid of a hydrofoil added to the motor doesn't appeal to me just yet. Prior owners were an elderly couple and judging by the condition of the boat, it may have been just a Sunday driver-putt putt boat for them. Immaculate and low hours.

Just looking to the more experience to see if all my internet reads has me going in the right direction or not.

Thanks,

Steve

[Hoey]

When operating my boat, too much trim results in porpoising. When this happens, I trim down a bit until it levels out. My trim gauge only covers the high torque range (lower gear of sorts) of the full trim.

[fishnowworknever]

Geez I wouldn't try and add any hook to the transom. You should really do what you mentioned and check the anti-cav plate when up on plane cruising before anything else.

Check this out from another forum:

This is a before and after shot of a customer that raised his engines 1 hole because they were too low.

The Brave fella that hung over the back to take these pictures is "The Pig" on TheHullTruth.com (Thanks)

Looking at the first picture, you can't see the antivent/anticavitation plate. Its under the surface and has whitewater rushing over it. This steals speed, rpm, and economy from you because of the added drag of the engines. It can also cause other issues like porposing easily, and too much bowrise during holeshot

In the second picture you can see the antivent/anticavitation plate riding right on the surface of the water. It may have a little splash coming over it every now and then, but thats all. I believe he gained a couple mph and a little economy. Every boat is different. I've seen people gain 3mph from a 1 hole change, and i've seen people gain nothing. If you go TOO high, you'll ventilate the props easily, and possibly loose speed. These pictures are taken with the motor trim and speed the same in both.

http://i201.photobucket.com/albums/aa105/kenuwf/toolow1.jpg

http://i201.photobucket.com/albums/aa105/kenuwf/correctheight21-1.jpg

[hydro]

Steve,

Hope all is well out there in the wild west!

You gave some good info in your OP, the WOT RPM is right on, maybe a little high but not a concern. Weight distribution is a key factor here and you gave clues on how to test that. A 17’ aluminum boat with a 115 hp motor is fairly limited in tweaking setup so I’ll give some basic hints.

1. Leave everything as is and move weight around. Have your wife sit in different places in the boat and watch what happens at various trim settings. Does the porpoising change? That will give you an idea how to better balance the boat. This is the most simple change and does not cost anything to try.

2. I agree that you could raise the motor one position and possibly get better performance. The “cavitation plate” does not have to be even with the bottom of the boat, and when on plane it is not even a relevant concern. Try raising the motor one hole and see if things change. Be ready to do the weight distribution experiment all over again. (High speed boats use this concept very effectively, but it is most effective at 70+ speeds)

3. Do NOT try adding hook to the boat as it will ruin performance. Also, the hydrofoil idea only has effect on hole shot and should be completely out of the water when planed out.

Give these ideas a try and post back with the results.

Hydro

[Raider4ever]

...hasn't allowed me to hang over the back while on plane to check out the anti-cavitation plate and see where that is riding.

I wouldn't suggest that.

Sincerely,

Pelle Lindbergh

[Kyhl]

Another thought, is the guage correct? I know my original trim guage is way off.

Then again, I find my alumacraft rides best without much trim so I propped for that with very little rake.

[Dragonsm]

Appreciate all the feedback and ideas/tips.

Not looking so much to cure this porpoise from a performance standpoint (max speed) but from more of a point to having the boat take the impact of waves a little more on the bottom instead a bit more in the front/nose.

I was able to get the boat out this past weekend with my neighbor for a day of fishing. 2 guys, a couple tackle bags....nothing to crazy overloaded.

Early morning launch we had a nice 5 or so mph wind with a little bit of a walleye chop. Boat responded as it had in the past with a little bit of trim. I kept an eye on the gauge and it was a little less than quarter on the gauge. (haven't compared it to where that actually positions the outboard yet, but I know it wasn't much)

Didn't think much of it after that as it just felt good to get out on the water.

The sun decided to come out and the wind died so we called it a day. Livewell (located directly in front of the consoles) was filled to keep minnows alive. On the run back to the landing I decided to play with the trim again since the water was glass. (first time I have seen this in SD)About the only thing different was the livewell was filled this time. Any trim what so ever, caused it to porpoise and it would progressively get worst if I left it trimmed the way it was)....only way it would ride is trimmed all the way down.

First thought is to play with some of the weight and move it further back. (Possibly relocate the battery at the console to the rear of the boat) Also, been keeping my eye out for a 19 pitch Yamaha prop to toss on there and see what she'd do to get the RPM's down a little. (6-6100 is bouncing it right off the ceiling of what the manual calls for)

I did take a closer look at the mount holes on the back of the motor. To me, it may look like it was mounted one hole lower at one point in time possibly.(thus raising the motor) Hrmm.....

Well, that is the update from what more I found out from this past weekend.

Guess I just need more "water time"

[fish_eat_sleep]

I have little Alumacraft.. I can get it to bounce if i want, or ride flat and smooth. Not sure how much there is to gain with trimming up on a sub 40mph rig. I don't see many benefits unless your running long distances trying to reduce drag for fuel reasons.

For what its worth heres my experience.

My boat at best gains 1-2 mph from trimming up. In any chop you can feel the lightened ride and the "slap" from the chop, even get airborne spearing big waves but most of the spray is directed out and behind the console. leaving the motor further down allows for better handling in chop, less bounce and "slap". Basically I have a valid preference for both.

As far as weight distribution goes I notice it a lot more if I have weight in the rear. moving a passenger to the forward seat levels it out. Preventing the bow from doing what it wants. most of your weight should be in the middle, at or slightly behind the console but more weight to the rear won't help.