Need Advise on 620 Porpoising

[JBlanck]

I'm sure there has been a lot of discussion on porpoising but I just came back from a one week trip with the family and one week on Lake of the Woods fishing, and I had a lot of problems with porpoising. I have an '07 620 with an E-tech 225ho. The prop is a 4 blade Cyclone 21 pitch. I have owned boats since 1990 and have never had a problem operating a boat and being able to trim properly to get the boat to perform in just about every condition. I'm struggling to get this rig to "cruise" down to 30-40 mph. At 40 mph (4500 rpm) the boat is smooth as silk. When I tried to cruise with the family or save gas on LOTW, it would porpoise at every trim location...even when the motor was trimmed almost all the way down.

Do I need a different prop or something? The boat was loaded evenly front to back and was even heavily front loaded with gear while going into camp and I could not go below 40 mph without porpoising. Please help me figure this out as I love the boat for fishing but this will drive me crazy.

Thanks in advance.

Jeff

[BroadwayBill]

Jeff,

Someone will chime in here for you. I had a 06 with a F250 Yamaha and had the same problem. That motor is a little to much for that year boat but you shouldn't have any issues with your motor. My guess would be that someone will mention your motor height and a different prop for you and it is quite likely one or both of those to fix your issue. I put an edge hydrofoil on mine because it was next thing to trim tabs and it solved my issue completely. I would do motor height and prop if you can first. Maybe you can tell us what hole the motor is mounted in.

Bill

[jet man]

call ricky at the prop shop in brainard mn and he will help you i an sure

[PJM]

Jblanck
Sent you a PM

[REW]

JB,
The best long term solution for your rig, is as was posted somewhere else by a different boat owner - to install fully adjustable trim tabs on your boat.

Then, depending on boat speed, load, balance, weight, etc. you can dial in the trim tabs to keep the boat performing perfectly all of the times.

Your situation is exactly why fully adjustable trim tabs have been developed. i.e. to be able to dial out issues that happen on a boat at some speed, some weight, some balance in the boat.

http://www.bennetttrimtabs.com/

or:
http://www.lencomarine.com/index.php...-tab-kits.html

Many many boat owners of all different brands have been adding trim tabs to their boats to give them a better planing attitude at speeds other than wide open, to keep the bow down when planing out or a myriad of other boat issues.
Motor heights can be changed, and props can be changed, but these changes can not accommodate the necessary needs of a boat and its owner at every speed from 0 to wide open.

But with the addition of fully adjustable trim tabs, the tabs can be adjusted for every speed to give the boat and its load the operation that is needed.

REW

[popi]

Where is your cavitation plate in regards to your hull when motor is full down?

[THROWINWOOD]

Pm sent

[p0007]

I have a 619 with a 200 and a 8hp kicker, I had the same problem after I added the kicker and put larger 31 series trolling motor batteries. I tried everything, putting weight in the front (not desirable) to a multitude of props. Even had a prop custom reworked which helped the most but when i put 3-4 people and/or filled the live well it still porpoised. To be honest I was ready to sell the boat. Since I use the boat alot with 4 people and gear, my dealer recommend the cobra edge hydrofoil I reluctantly put it on (as i tended to agree that it is a band aid for a setup problem). It is amazing the difference, it is like an brand new boat. I can cruise at 31-33 at 4.5mpg. I can trim out to the 3/4 line on the gauge to get the bow up out of the water at 31mph vs before I was trimmed full down until that 38-40 mph range. I actually gained 2 mph on top end with 4 people in the boat and the boat rides up out of the water and doesn't feel like its plowing anymore and it rides better in rough water. Band aid or not, it was a cheap solution and the boat works perfectly now which is what really matters! One caveat, I have a few different props, the stock yamaha props worked best for me with the foil, the merc tempest reworked worked best prior to the foil, and didnt work that well at all with it. Not sure why on that one? It was the most efficient from slip % standpoint before and the worst after.

All I can recommend is start trying the easiest fixes first and see what works. I think that the new 08 and newer hulls are much less prone to this than the older hulls due to the redesign characteristics. They just seem to be more sensitive to weight distribution. There also seems to be some variances in the performance from hull to hull possibly. There are so many factors that can affect this that you have to simplify and start from there. Good luck, I know how frustrating it can be.

[JBlanck]

What do you guys think about jack plates to help this situation? I know it's expensive, but it could help in adjusting for different conditions. I just don't know if that is the main purpose for jack plates.

[p0007]

My boat has a 5" setback cmc manual jack plate, regardless of height I adjusted to it didn't help much with porpoising. In fact I wonder if it made the problem worse because you are moving the weight of the engine back 5in from the center of gravity. So you have to multiply the weight of the engine x the distance moved to get the new moment it creates on the boat. I.E. it increase the effective stern weight (lever effect). Not sure what affect you would see on your setup with one. I do like having the ability to adjust height easily, and the setback I think gives me a 1-2mph over no jack plate. Has your boat always done this since new?