Need ideas to stop porpoising?

[gofastsandman]

Bushwacker borrowed my mirage + and plotted a performance chart. I expected to lose in hole shot, min speed to plane, midrange, mpg, and handling. The 4 blade also beat the Mirage + top end! This was deflating. Contrary to my p brained belief. More drag = higher top end?

My `89 20 sf {c.c.} is running a `96 ocean pro 150 @ 365#s. I had a Mich rapture 14 1/2 x 17 BOW lifting prop. On the hole shot my bow would rise to the point of almost losing sight of the ocean b4 planing off while standing. My cav/vent plate was also 3/4" below the keel which would tend to pull down the stern as well.

The mirage changed the whole dynamics of the boat, and that was b4 I moved the motor up 1 hole. It used to slap the chop, now I slice it. The angle of attack is MUCH more acute. The hole shot lifts the stern and the bow shoots forward ,not up! I dont use nearly as much negative trim to keep her down while running , and I picked up a couple mph top end. Lost a little grip trimming up and would blow out sooner.Moved the motor up and got some rpm and more top end. 3 mph total 2 way gps. No tabs or Bimini on....yet.

[gss036]

Thanks for all the replys. Lots of information to think about. YES, I did have a stingray fin on the merc 200. I had thought about installing it but it does not look like a good fit to the honda. I saw on WestMarine site that they have a new type fin that installs w/o drilling but is 249.00. I ABSOLUTLY cannot go w/o my 15 Honda for a trolling for salmon fishing.
I had thought about the batteries, but that would take major work to do that, definately a good idea though.
I haven't tried top speed yet but I think it is going to be in the mid 40's as I got 44mph w/the 200 Merc. I only have 10 hrs on it now and I did run it up to 5K and was sitting at about 42mph. The last 3 trips have all been in 2-3ft chop so speed was not an issue there.
I like the idea w/the trim tabs, I will have to try it next time out. I was wanting to get out a couple more times this week but plans changed dramaticaly this morning, spent all day at the hospital w/wife and her 98 YOA mother and things are not looking good there, so I know where my time will be for a while now.
I will get back on the water ASAP.

[strick]

Lots of good advice. I hear you about not wanting to remove the kicker. Having that extra insurance on your boat is nice . I think Briguy is right on with his advice by trying the prop first then if that don't work put on the doel-fin. Those would be the two easiest things to try first before going to the extreme of moving fuel tanks batteries etc.. Bushwacker is right on about the bracket. Sorry to hear about your mother in law. At lease you have a salmon season

strick

[eggsuckindog]

Raise the motor, I will bet its too low which drags the Cav plate, do that first. Never heard of a WA with this problem but thats alot of weight if everything is still back there I guess.

[FELLOW-SHIP]

I have trim tabs, but hate to use them as the do slow you down 2-3 mph.

Hi Gary;

Been reading all the good info which is all very valid but you are avoiding using the TABS which is the answer to your problem. All boats designed and made from the factory are tested with light loads and no extra weight. As time goes on we add and change all kind of things. Shift weight and adding stuff like kickers and 220 Lbs. for today’s newest 4 stroke motors, large live wells and what ever else we think is cool. Gary you need to look at Tabs like pilots look at flaps on a plane you just need to use them to control your boat the way you want it to run.



Fellow-Ship


Just for the Grins

[Captainkass]

Hey G, do you have a long shaft on your new motor if so this can cause some porpoising if its not the right height in relation to your transom....

[gss036]

I was out again yesterday and it was a fairly calm day, had two of my late-teen grandsons w/me and I had moved a total of 60#'s of lead to the front of the boat. To my surprise, the porposing has just about (90+%) gone away. The first few trip we had a lot of chop and rolling water and that may have had more to do with it than anything. I did lower the trim tabs slightly, don't know if the were even or not had not set them prior to going out. As soon as things calm down around here and I have time I will dig more until the problem is solved.
I know I had a friend who had a Wellcraft w/225 Suzuki on a bracket and he had really had a lot of porposing on his boat. He has since sold it so I doubt if he ever solved the problem there.

[paragod]

Can u post a pic of the cav plate in ref to the transom ? take a side shot. .5 to 1.5 above the pad. look and see if there is a tiller pin in the transom bracket make sure it is in the bottom hole Iam not a Honda Mech but Iam a Merc and you can run the mercs withit out giving u more negative trim to help put the bow down. I run a Hydro with standard water pick ups 2 inches above the pad with no water preasure loss. I see u had a 200 merc before and the performance looked pretty good. If so cool I have a 200 merc I can slap on my new to me 23 CC and get it wet faster than new power .

[Fr. Frank]

The shape of the prop can greatly affect porpoising, as well. A bow lifting prop with a boat with very little rocker in the hull will induce porpoising. Changing to a stern-lifter prop can help greatly. Judicious use of trim tabs is also a very good idea, as is carefully watching trim angle and mounting height of the engine.

[gss036]

I talked w/the mngr of CapSante for quite a while yeaterday and he did an excellent job of patornizing me and saying my suggetion on a bow raising prop and raising the motor was expensive so, I can see they are not going to be any help. He did say that Honda does not like other mfg's props on their motors. Looks like any fix will be out of my wallet. Although he did suggest a whale tail or doel fin, said he has seen them om the big Hondas. He did say he would check on that and get back to me but I am not holding my breath. They already have been paid for the motor and installation.