Hydrolock prevention, 1999 VP 5.0 GL- odd question

[Augoose]

All,
I know this may sound ridiculous, but I'm looking for ideas to prevent my 1999 Chris Craft 200br with VP 5.0 GL from hydrolock which has happened twice now. In short, I've owned the boat since 2012 and never had issues until last year. Something of importance is that one year prior I added a fiberglass swim platform which weighs about 250 lbs. I think that has aggravated the issue.

So last year we were moored off a beach in rough water. The boat surged up and down more than it has ever in chop for about 2 hours, so much that air and water were blowing through vents in the swim platform like a whale purges air and water out it's air hole. On the way home that day the boat was hard to start and the boat completely shut down while underway - a surge of water hit the stern and I couldn't start it after that. I was towed in and then drained water out of the rear cylinders on BOTH sides. Manifold gaskets were new the year prior.

Fast forward to this year and after replacing a litany of components thinking I had an electrical problem the year prior which contributed to the stall and surge of water, we went out on the water and the boat ran great on several outings.

Last week we were moored again with bad chop. Again, blow hole surges of water from the swim platform vents. Myself, my wife and my two boys were all sitting on the back deck while swimming. Went to start the boat and it was hard to start - it stumbled, coughed, and bogged for several minutes until it eventually cleared up. Seemed very similar to last year.

I'm thinking the weight of the added swim platform plus the four of us sitting on the back deck caused the static water line to drop, going below VP's 14 inch requirement. This caused the water level to rise where water worked it's way up the exhaust and into the engine. During other trips this same season with calm water, we haven't had any issues.

So here's my question - where are the exhaust passages through the exhaust on a SX-M drive? I know about the prop, but what about other areas around the transom? The exhaust bellow is in good shape with no cracks that I could see. I replaced it in 2012.

What if I were to make a sock or boot which I placed over the prop while anchored to prevent surges of water from working its way up the exhaust? Obviously I would have to create some sort of reminder procedure to prevent forgetting the boot before starting the engine. The risers I currently have on my manifold are already pretty tall, so I'm not sure a taller riser is the answer.
Thanks
Augoose

 

[Lou C]

VP and aftermarket exhaust companies sell 3” risers for this style exhaust for that reason. Might want to consider this if you have enough room to do so. I would because sooner or later hydrolock will cause serious engine damage.

 

[QBhoy]

Hi. I could maybe almost understand this if you said it was hard to start after the modification. But you mention that it stopped the engine whilst the engine was running and underway ?? For me, there is no way this happened as a result of taking water in up through the exhaust. The pressure of the exhaust when running would overcome any surge of water when underway travelling forward. I’d think anyway.
Are you sure something else isn’t going on ?

 

[Augoose]

VP and aftermarket exhaust companies sell 3” risers for this style exhaust for that reason. Might want to consider this if you have enough room to do so. I would because sooner or later hydrolock will cause serious engine damage.

Thanks Lou - I already have 4" risers. My engine sits really low in the compartment. Looking to block the water from coming in.
Thanks!

 

[Augoose]

Hi. I could maybe almost understand this if you said it was hard to start after the modification. But you mention that it stopped the engine whilst the engine was running and underway ?? For me, there is no way this happened as a result of taking water in up through the exhaust. The pressure of the exhaust when running would overcome any surge of water when underway travelling forward. I’d think anyway.
Are you sure something else isn’t going on ?

The engine died last year while underway and the surge of water forced its way up the exhaust. Now I think the problem is the boat sitting too low in the water and waves forcing the water up the exhaust.
Thanks!

 

[Scott Danforth]

Measure your elbow to waterline height. The bottom of the elbows must be 14" above the static water line.

When you added the swim platform, that 250# weight is outside the transom. Its effect is like adding 600# over the engine. When you add 3 or 4 people on the swim platform, its effect is like adding 1500# over the engine.

Its a simple physics issue. You are pushing the motor farther ino the water

So measure your static waterline......

You may find you need to add another 3 to 6" of riser to compensate for your added swim platform and people on it

 

[Bondo]

What if I were to make a sock or boot which I placed over the prop while anchored to prevent surges of water from working its way up the exhaust?

Ayuh,...... Water seeks it's own level,..... You added weight to the back of the boat, taller risers is the only cure,.....

 

[Augoose]

Thanks for all the help and sorry for the late follow up. I had a bad crash wakeboarding and dislocated my shoulder. Had surgery last monday and now I'm laid up for awhile.
Eventually I'll be back out at the boat and will measure the existing height of my risers and see if I can go higher.