Boat porpoising, need experienced advice

[Bass AHolic]

Is it against forum rules to post a link to another forum? I'd post pictures of my boat restoration but I'm too worn out after posting all of them on the deer hunting forum that I frequent. LOL

nope. just don't post politics, and for sale stuff w/0 giving Al some $ for advertising. maybe good to go then.. But posting pics is a PIA in last few years. downsizing the pixels etc.. I'd rather go fish for carp with popcorn.. then mess with that change size stuff haha

[Bassman Ia.]

Unless I missed it, which outboard and size? Maybe that aluminum prop is flexing or it has a spun hub.

Bow lift---- A SS Raker gets my vote

[Fatshaft Merc]

You've added weight to the boat and your current prop can't lift and carry the boat anymore. You do not need more weight up front. What motor and prop/pitch? Aluminum or stainless?

[FurFlyin]

115 Yamaha V4. Aluminum prop. I don’t know the pitch, I’ll try to get that and post it this afternoon

Here’s a link to the refurb and transformation. I figure I’ve got 125-150 hours of labor in it. I did everything myself, except the paint. I got the paint guy at our shop to spray it. I know my limitations. LOL

http://www.aldeer.com/forum/ubbthrea...95#Post2437095

[hatcreek]

You've added weight to the boat and your current prop can't lift and carry the boat anymore. You do not need more weight up front. What motor and prop/pitch? Aluminum or stainless?

With the mods the OP mentioned (all the weight added forward), this would be my guess as well... About the time it starts to carry the nose, it falls off.

[Bassman Ia.]

well looks like you did a great job with it.

As for the problem----I think it's your prop. I realized if you move 160 lbs to the back of the boat it will change things---- but i think that amount can be handled in a 17 ft. boat without creating problems

[FurFlyin]

Thanks Bassman. It's an 18' 6" boat, not a 17 footer.

Here's a picture of the motor while running. I have a video, but I can't figure out how to shorten it on my phone to the point that I can email it.

Do you guys agree that the motor needs to come up? There's a hydrofoil on the motor, but it's submerged enough that I can't see it. This may not fix the porpoising, but it's still not correct AFAIK.

[fastman151]

I saw the pics of your restore...really nice job, kudos to you!!

Am I right in assuming that when you reinstalled the motor, it was in a lower position than when you started this project? If so then it is not just about relocating the TM batteries. I'll go out on a limb and say you're probably not hitting the same rpms as you were before!

[FurFlyin]

Thanks fastman. No, the motor is mounted in the same holes that it was before I removed it. 2nd from top. I started to raise it a hole when I reinstalled it, but it ran so good prior to the restoration that I put it back where it was. I didn't think about the stern being deeper in the water from the added weight.

Everything I added on the front deck was made from aluminum. If you add the extra aluminum, and TM difference, I don't think it would have added more than 50-55 lbs. The 1/8" plate weighs 1.76 lbs per square foot. I added around 20 ft sq. I also added some "legs" under the deck for added support. Those were 3/8" x 3" flat bar @ 1.32 lbs per foot. So another 5-6 pounds. Then the added weight of the Ulterra compared to an old 12 volt foot control MG. Only thing I stored up front was life jackets a throw cushion and a fire extinguisher.

[hatcreek]

Hope you can get the problem diagnosed/rectified... The right SS prop should be a big help.

Just looked at your restoration post... Very nice work.

[Rob4AU]

I didn’t read all the post but I can assure you the Xpress boats set up properly will not propose to the point it can’t be corrected with set up. I currently have an X51 with a 115hp optic and a x19 with a 225 optic and both will run without proposing. Both have jack plates and stainless props and I did run several props before settling on one but I never had a porpoise issue with any of the quality stainless props. Before anyone tells me they are both overpowered I am fully aware of it.

[FurFlyin]

Thanks for all the help guys, and for the compliments on the restoration. Does any of you have a solid "this prop will work good on your motor" recommendation, or is that even possible? I'd order a stainless prop today but I know absolutely nothing about them.

[bulldog44]

My boat looks identical to yours but for mine has a 90 hp Yamaha and is a 1998 H51, 17'.
I would recommend a Turbo 1 prop, not sure on the pitch you need. I went from a Stiletto 15p to a Turbo 1 17p (based on info read here on BBC). I had some porpoising with the Stiletto, So far I have not seen the porpoising problem as before, but then I have not been able to fully test it (weather keeps me off lake). I also do not have a jack plate, motor mounted straight to transom. I did move two anchors upfront, and to the passenger side and that helped, but that was with the old prop. I'm running all three batteries in the back. Overall this new prop holds better in turns, and cruising speed is great.

http://www.yamahapropselector.com/propSelector/web/ to select correct pitch for your boat.

[kry29]

I would get a stainless prop. That aluminum one might be flexing. Really nice job on the restore too. That thing looks great

[FurFlyin]

The prop that's currently on the boat is a Solas 13x21 aluminum

[adchunts]

Just throwing this out there...

I had an Xpress H56 (18 footer) with a Yamaha F115 on it. If memory serves me correctly, it was a 2006 model. It porpoised the entire time I owned it. Spent hours on the phone with dealer and factory to try and figure it out. They finally recommended having a welder put a bead on the pad in a couple of specific locations (do not remember exactly where). The issue was not something unfamiliar to them. I used some marine epoxy and mocked up the size and location of the recommended weld beads, and it did seem to help. Hit a t-post on a local lake shortly thereafter and drove it through the pad and ripped the transom, so never got any further.

[rchavis]

I bought an Xpress this winter and just finished up a complete restoration with some modifications. I extended the front deck with aluminum to come back to meet the front of the console. I also added a 24 volt Ulterra up front. Prior to beginning the restoration, I took the boat out and it ran great. Got up on the pad and rode like a dream.

When I bought the boat, the trolling motor battery was up front, under the deck. I installed 2 new batteries and an on board charger in the rear compartment.

The boat no longer drives and rides great. Now at WOT if I trim the motor up enough to get the bow and speed up, the boat begins to porpoise terribly. It won't power through it either. I'm having to run the boat with the nose down, which is killing my top end speed.

I do not have a jack plate on the boat. After spending a war pension on the refurb I can't swing one right now either.

Would raising or lowering the motor help?

Any advice?

Have you tried posting on the Tin Boat Forum . Use to be a lot of Xpress Boat set -up info there one time or the G3 boats .

[mrc]

Weight distribution problem. Either trim down or redistribute the weight.

[Roddy]

Most likely a prop with more cup will fix the problem. Do not add more weight to the front as you already can't carry the weight up there now.

[John Jackson]

Most likely a prop with more cup will fix the problem. Do not add more weight to the front as you already can't carry the weight up there now.

+1 here. You probably were not lifting the bow with the battery up front. Now you are lifting the bow but your setup won't hold the bow up. More cupping or a prop with a lot of bow lift, like a tempest, should help.
Also the guy with the weld bead is hitting on something common with aluminum boats. The pads flex and don't work as well as fiberglass pads, and the weld bead can give a bite that can partially compensate for the flex.