Another 25 Seafari goes under the knife

[cdavisdb]

Mounting your tabs as far outboard as possible might create some unexpected issues. Outboard maximizes their effectiveness, but makes them subject to coming out of the water. Probably not a problem when the boat is running, but at rest, it might noticeably increase the roll. Mine often rolls the outboard hull panel out of the water, especially if it light loaded. You may find that the roll characteristics change in unpredictable ways when the tabs clear the water. I'd be very interested in what you find.

[Blue_Heron]

Originally Posted by cdavisdb

...but at rest, it might noticeably increase the roll. Mine often rolls the outboard hull panel out of the water, especially if it light loaded. You may find that the roll characteristics change in unpredictable ways when the tabs clear the water. I'd be very interested in what you find.

You know, Connor, I hadn't thought about that. The tabs on my other two boats are well outboard, but their chines don't rise much out of the water when rolling at rest. But rather than outboard tabs increasing roll, I wonder if yours are damping roll because they're mounted on the center panel and remain submerged at rest and should provide resistance whether rising or falling.

Dave

[seafari25]

Hey Connor,

Maybe I'm misreading what you said but my tabs are still effective, even when I have her pinned, although I have the extensions. Are you talking about wot, cruise, hull speed or on a drift? It's interesting to learn how other setups perform. I would think your tabs, mounted closer to the keel, would be more effective. I think Dave will be modifying his tabs, similar to my Grandfathers so maybe he wont notice any issues.

Nice work, Dave! Please forgive my ignorance but I have never seen a drain hose attached to the oil pan. We always suck the oil out from the top. Are you able to gravity drain the oil or do you suck from that hose? I guess I'm still stuck in the 70s.

Brandon

[Blue_Heron]

Originally Posted by seafari25

... I think Dave will be modifying his tabs, similar to my Grandfathers so maybe he wont notice any issues.

Brandon,
I will be modifying my tabs. My extensions aren't as wide as yours, but they do follow the contour of the step in the hull. I'll post pics when I've got them bolted on. I don't know what effect they'll have on roll characteristics at rest, though. Time will tell.

Originally Posted by seafari25

Nice work, Dave! Please forgive my ignorance but I have never seen a drain hose attached to the oil pan. We always suck the oil out from the top. Are you able to gravity drain the oil or do you suck from that hose? I guess I'm still stuck in the 70s.

Brandon

The hose has a cable on the end that attaches to a swivel on the garboard plug. So you pull the drain hose out the garbaord plug and gravity drain it.

Dave

[seafari25]

Thanks Dave, that makes it a lot easier to change the oil. Great idea.

Looking forward to seeing your tab extensions.

[Blue_Heron]

Originally Posted by seafari25

I think Dave will be modifying his tabs, similar to my Grandfathers so maybe he wont notice any issues.

Going back a ways here, but I need to give credit where it's due.

In email conversations with strick and Bigfluke over the past two years, it's apparent that the 25 Seafari needs plenty of trim tab authority to function well. For most boats, the closer you can mount the tabs to the chine, the longer your moment arm, and the more effective your tabs will be. But the outer step on the 25 Seafari is only about 9" wide, so if you go as far outboard as possible, only the outer 9" of your trim tabs comes in contact with the water as you start to lower them. As an illustration, here's the port trim tab on my 20sf:



The trim tab isn't much wider than the hull panel, so most of it is in contact with the water as you begin to trim it down. Contrast that with the trim tab on the 25:



On the 25, a significant fraction of the width isn't in contact with the water until you trim it down about 50%. This video is very short, so you may have to play it a couple times, but you can see how the water on the inboard side of the tab is out of the water:



So what is the solution? Well, Brandon's Gramps came up with a good idea. He scabbed a metal plate to his tabs that would follow the step in the VDR hull:



I thought about doing the same thing with some SS sheet metal I had, but I didn't think my material was thick enough. And trying to bend SS sheet to match the hull would have been no fun at all. So I decided to use my recently acquired fiberglass fabrication skills to make some trim tab extensions. I'm happy with the results:



You can see in the picture that I added a SS angle at the outboard edge to catch spray and channel it back along the outer edge of the tab. I'm not sure if it makes the tab extension more effective, but it does stiffen the edge of the fiberglass panel. This video shows the tab extensions at work:



There is a noticeable difference in performance. Trim tab response is much more pronounced. I was playing around with trim on the river last Sunday. With the tab extensions, I got the boat to stay on plane at at 13 mph with less bow rise than I was getting before at 14 mph. It's actually pretty sweet.

More to come... I'm doing the prep and finish work on my swim platform and engine cover. I hope to get those both done in the next week or so. I also need to get my VHF and stereo installed. The VHF for obvious offshore safety reasons, but it's a tradition to listen to classic Buffett when we're trolling for Dolphin, so I've got to get the stereo done in the next couple weeks.

Dave