Conversion or ????

Hello.
I own a 70's 16 foot Kona which I dearly love, but I've had some problems with my current motor.
The boat is currently powered by a "massaged" 115 horse Mercury outboard.
Though I love the way my boat performs and handles with the Merc, I have a problem with cracking in the fiberglass above the transom.
The transom itself is sound, but the top glass does not have wood behind it, and cracks due to the transom flexing caused by my driving the boat like a maniac.
Though I do not endanger other boaters, if the lake is clear I love running way too fast across rough water, sometimes catching quite a bit of air (becoming airborn). I know, it's dumb, and dangerous, but it's what I like, and they won't let me drive Miss Madison.
The cracks do not weaken my engine support, but look bad, and I think they might cause me to hold back sometimes when I'd much rather be blasting across waves.
I'm considering converting to an automotive type engine/jet pump arrangement, even though I outrun jet boats regularly.
Will my style of playing create new problems?
I'd rather have unsightly cracks in the cap over my transom than have my engine fall through the bottom of the boat, and as I've stated, I play very rough, so it could be a consideration.
This boat is on the water every week-end and sometimes several times during the week in the summer. So far I've never made it past mid season before the cracks appear (I've owned the boat for 25 years, first owner had cracks too, which is why he sold me the boat).
Is this conversion a good idea, or would I be better advised just to keep fixing the cracks every winter?
Perhaps someone knows a way I could make the cracks quit happening (other than driving like I had good sense, which aint gonna happen).
So far I've tried using heavier glass mat, but this just causes "bullseye" stress cracks in the gelcoat at other locations on the cap, and it eventualy cracks again anyway.
Thanks for any help, or advice you'd like to give, with the exception of SLOW DOWN, cause like I said, that aint gonna happen.

 

Generally way cheaper and almost always more successful to either stick with what you've got or sell it and buy something that suits your needs better.
If it's top speed and good rough water performance you're after, I'd leave jets alone - you'll be better off with the o/b

 

Hi Willallison!
Thank you for your reply.
I really am quite fond of outboards, and I've spent years getting the most out of Merc powerheads, so I do know them rather well.
Your right about jets not really doing very well in the rough I think, as they do not stay with me across whitecaps, nor do they seem to run well over about 65mph or so. I've had a few that seemed hard to stay with till we got into the serious top end, but practicaly none that could keep up when I went WFO, save for all out race boats, and they avoid rough water like the plague.
My old Kona is like a part of myself though, so what-ever it takes, she'll be staying with me.

 

If the outboard is working well for you and you love the boat, maybe the thing to do is to consider reinforcing the transom with some sort of extrusion inside to attempt to reduce flexing a bit and also reinforce the top deck, from beneath (difficult yes, but not impossible).

You didn't happen to ever take a picture of the cracked deck did you?

Without having a picture of the cracked section, as an easier to construct way out, I wonder if you could get away with creating a new replacement inset deck section using more flexible epoxy (since the old Polyester gets more and more brittle with time) for the affected section. Not sure if that would be an option for you aesthetically - depends whether authenticity and finish or weight savings is more important to you.

 

Dogpaddle;

I think your problem is caused by the weight and angular moment of inertia of the outboard. When the boat slaps on the water it creates high angular rates. The angular moment of inertia of the engine resists the these high rates which causes high stress in the transom. The fact that this area is cracking indicates that it is a critical load bearing area and you are going to have a problem is you don't fix it.

Converting to an inboard should resolve the problem, but that would increase the weight and CG location, so it would be a major job to get trim right. I doubt it would ever run as well as it does unless you hired a naval architect to help you $$$. As Will said the best approach would be to change boats.

Jeff's idea of reinforcing the transom is probably the best approach.

If you want to run at 65 mph then your best bet would be a surface piercing drive although your power level is a little low for Arneson drives. The surface piercing drive should beat the jets and most of the outboards.

Cheers;
Mike Schooley

 

Hi Jeff, and Portager!
Thank you both for your suggestions!
Now THIS is what I call a helpful board!
I grabbed my camera and went outside and took a couple of shots of the cracks so that you could see what I'm up against.
As you can see from the photo, the crack is happening along the seam where the top joins the bottom of the hull. I don't think the original design intended the seam to be glassed over, but that is the way the "boatwright" who fixed it for the original owner did it, so it has been done that way since. The cracks run completely across the stern, with one coming up the roll on top (I'll post a pic of that one too) .
This area has no support under it, so it's just a shell, but I like to keep water out of the transom, so I fret about it.
While taking the photo I noticed that the fiberglass mat exposed by the crack seems "dry" meaning that the resin that was applied did not fully penetrate the cloth...something to guard against next time it's repaired (and possibly a reason it cracked again?).
Though it is a classic, I'm willing to modify the boat in any manner that will help keep it from cracking.
Thanks again for helping!

 

Here is a pic showing the other side, and how the crack comes over the roll....more dry glass....wonder if I'm onto something here?

 

I know I'm rather late in the game (several years?), but have to make a comment. My family owned this exact boat when I was kid (also several years ago ). We bought the boat after the merc. was replaced with a 140hp o/b Johnson. The boat was scary fast, had a racing prop on it for a while that would kick it up on its side if speed was right, and the boat was making a bank to the left. The transom had a 1/2" steel plate bolted and apoxied in place. Story had it that the first engine did break free from the transom and this was the solution. Didn't look gorgeous but certainly did the job. I enjoyed many days on water beneath the Narrows Bridge in the Puget Sound catching air off of freighters...scary but soo fun.

Tested: The boat sank one time and was litterally resting on its engine. My dad and I hoisted it from its sunken grave and he had the engine rebuilt and running with in days.

I miss the Kona!

 

Inboards are much heavier and will make the boat loose speed. The CG will change and make the boat bow heavy. Also, the stringer and transom need to be modified for the mounts. How are you repairing the cracks? A patch usually makes a hard spot that may cause more trouble. A reinforcement system could solve the cracking.