TOPIC: Porpoising ??

I, had a porpoising problem with my 65 G3 when the new Merc 50 was put on my boat , Dealer didn't set it up right , cavatation plate was 4 inches below the bottom of the boat . I fixed that problem !! Raised the engine So I tried putting sandbags up front under the bow (120 lbs. ) That stopped the problem ... got it up to 5300 rpm no porpoising !!! Also moved the fuel tank up front, thats about another 50 lbs when full !! At this point ,boat runs ok But now I hear I should put wedges between the transom and the engine !! How do I determine which ones to use they have 2 degree 5 degree and different sizes also . The G3 has a curved transom , How do I set up the wedges and what degree angle am I supposed to acheive ?? If I put wedges in can I remove the 120 lbs of sandbags ????

tony... i think you'll get more of a response if you post this on the g3 forum. i sent the email to jim. ron

Could it be that it is trimmed out too far already? It sounds like my boat when I go too far. It either starts to porpoise or cavatate. Just a thought.
Bill

Same here. When it starts to porpoise, I just trim it down a tick and it smooths out.

Many boats have wrapped bottom shapes after all these years. The correct way to fix the problem is to take a known to be straight 6' long level and grease pencil where the boat bottom has twists, hollows, and bulges. If one get all of those out of the bottom. The boat will be faster after this attention, also.

Here is a pic of our G3 hull getting a tune up

I believe that the "wedges" you are referring to are shims. These are used to create a flat clamping area for the motor - when the motor is put on a boat with a curved transom. The shims eliminate the stress placed on the motor brackets when they are bolted to a non flat (curved) transom. The brackets also may not make enough contact to a curved transom without the use of shims. I don't know if they are truly necessary for your motor on the G-3. If the motor is new - find out if the shims are required to have the motor remain under warranty. I know of many people running motors on G3s without shims - but I can't say if this is the case for your situation.

As for the porpoising problem; I've never ridden in a G3 that didn't porpoise to some degree. Most do it at speeds exceeding 30 mph, and by the time the boat reaches 40mph it can be pretty bad. The heavier the ass of the boat, the worse it is. Keep in mind that these boats were pretty much designed for a motor of about 225 pounds on the heavy end. Most were equipped with engines weighing less than 200 pounds. The best solution to the problem I have seen work is the application of trim tabs.

Modern 4 stroke engines are really heavy compared to the motors these older boats were designed around. My 50's Evinrude 35 is about 125 lbs. My later Chrysler 45 is about 150 (the 35,45,50 and 55 is about the same), with alternator, starter and no T&T. Your Merc is around 250lbs. The extra weight makes a big difference. Moving the tanks to the bow and maybe the battery under the front seat is the standard thing to do.

Maybe this is an explanation of the "wedges" or shims that Bruce was referring to. When this transom was raised a PVC cap was put on the top for protection. That extended the width of the transom by about 1/8" just at the top. When the motor was hung the angle of the motor brackets to the transom was quite noticeable so pvc shims of the same size as the cap were put in place to distribute the motor "push" load. I've never done this on any other boat but without those shims I think it would stress the upper portion of the transom somewhat and cause the bow to plow or maybe cause a porpoise unless the motor angle was adjusted.