hydro shield? - Page 4

Fr. Frank · #31 11-27-2016, 05:26 PM

Original question was about the HydroShield. No, this amazing device will not help the tendency of the 25 to want to bank like a fighter jet in the slightest turn. But yours sounds like it's gone from being nimble to being downright twitchy. One is fun, the other gives you a tired set of Kegel and gluteus muscles.

I think several people here are on the right track with addressing the CG, both vertically and longitudinally. If you run with just a couple of degrees of down tabs on both sides it will help tremendously. Even when the hull leans/banks in a turn, it will quickly return to upright when the vessel is once again going straight. How many degrees of tabs you'll need to run you'll have to figure out on your own.

The only 25' I've ever worked on and had to block up was a twin stern-drive model, and with full fuel it had a longitudinal balance point about a foot behind the cabin aft bulkhead. It did have ballast bars below the cabin floor. We ended up putting two keel blocks under here plus two Brownell stands.

By contrast, my current '71 Seafari 20' with 140hp sterndrive balances fore and aft just 8' forward of the transom with no fuel. (I've never blocked it with fuel in the tank).

badhabit · #32 11-27-2016, 09:23 PM

thanks frank. it seems like it rides best with tabs all the way down. do you know how much ballast was in the one you worked on?

kmoose · #33 11-28-2016, 09:39 AM

I think there is something in the OP symptomatic complaint that points to a possible issue that has been overlooked. The symptom of tab, tab... Fallover is a classic symptom of non- baffled fuel tanks. Is the main tank new? What about the 40 gal in the stern? Are the symptoms just as pronounced when the tanks are full? Just something to consider....

Bushwacker · #34 11-29-2016, 11:42 PM

I think Gillie and Ken nailed it with the fuel sloshing/tank baffle comments! 120 gallons is a BIG tank that should have several baffles in it.

When a boat is already marginally stable in the roll axis, an un-baffled tank would tend to make it highly unstable because a little bit of roll shifts fuel weight in that direction, causing more weight shift which causes more roll, etc. A total of 160 gallons of fuel that's free to go where ever it wants to is almost a half a ton of mass that you have absolutely no control over! A 400 lb cooler in the cabin is a nit by comparison! Imagine having a roly poly 500 lb passenger free to roll around on the deck that immediately rolls to the low side as soon as you start a turn! I'm surprised you're even able to control the boat at all! Kinda like trying to balance an anvil on a broomstick!

Did you notice any difference in handling between when the tanks were completely full and maybe after you burned off ~ 1/4 tank? The mass can't move around when tanks are completely full, so I could see you starting off the day with the boat handling fine and then gradually turning in to a nightmare!

cdavisdb · #35 11-30-2016, 08:15 AM

Non baffled tanks would explain a lot, but not the bow up business. More than one issue?

kmoose · #36 11-30-2016, 09:53 AM

Quote:

Originally Posted by cdavisdb

Non baffled tanks would explain a lot, but not the bow up business. More than one issue?

I bet with an empty rear tank and 30 gallons in the main it's a different boat. I would do lots of experimentation starting with fuel weight.

badhabit · #37 11-30-2016, 04:31 PM

This is the boat

cdavisdb · #38 11-30-2016, 04:52 PM

Good looking boat

Is that ruler in inches? Is that the normal trim angle that you run at? Can you post a pic of how the prop direction lines up with the keel(at right angles to the hul)? So we can see if it is trimmed in or out.

If its inches, and comparing to my I/O drive (a lousy comparison) it looks to be trimmed too far out, which would make the bow ride high.

badhabit · #39 11-30-2016, 05:41 PM

I am not sure if it is in inches, the boat is kept at a friends house and I just grabed a t square he had. I will try to get better pictures this weekend starting with the motor all the way down. as far as the fuel tank the tag on the big tank says 2004. I think the smaller one is the same but I will have to check. the last time we took it out both tanks were full and it might of been a little better or I might just be getting used to it. my son is 25 years old and is a commercial diver and has been around boats all his life and he wont even run his own boat. lol

badhabit · #40 11-30-2016, 05:50 PM

kmoose, on sea trial back tank was empty and the big tank had about 15 gal in it. it was flat calm and it ran great.