Spray patterns, 21 and 25
 

I've always been puzzled about why my 25 is so extremely dry riding. It sure doesn't look like it should be, with such a sharp and vertical sided nose, hardly any flare. Watching Moose's videos of Dave's 25 and Terry's 21(Gathering thread, page 10), I got a few clues(thanks Moose). I'm not real well versed in the technical aspects of this stuff, so would appreciate some feed back.

Looks like chine position and shape is key. Watching the 25 run in small chop, the hull throws spay out and back. In relatively flat conditions of the video, it exits the hull way back from the bow. I've watched it running in rougher condition and that doesn't seem to change,at least until its too rough to watch. The chine must be at just the right angle to deflect spay outward as it comes up the hull side. Since the chine rises fairly high at the bow and goes essentially all the way forward, it must continue to do the same deflection as the waves get bigger. That deflection keeps the spray away from the windshield, even in a moderate cross wind.

The 21 doesn't have that chine forward. In low chop, it looks like the 25, the front of the bow is riding above the waters surface, spray is thrown back, out, almost down. In a little bigger chop the bow starts to spit the wave and the spray pattern changes, getting much more vertical. Bushwacker said the spray went up vertically when the 21 hit a big wave. That's consistent with what I could see.

Another fascinating question is comparative rides of the two hulls. The the 25's chine has to provide some lift and make for a harder landing than without it. With no chine and a super sharp bow(sharper than the 25, believe it or not) will the 21 provide a softer head sea ride in the nasty's, even though its smaller and lighter?

I think it depends on where the wave is hitting the hull at the time. I also think the 25 stands a way better chance of bridging the gap on stuff like we were in Sunday. I plan on mounting points on the side of my rig to get more stable video like that taken from the windshield mount the next time some of us can get out together.

I edited the original to show just the Seafari running along side.http://youtu.be/K4E1yGq6q50

The bow of the 25 is pointier above the chine than the 21 and hangs way over the point of entry. More flare too. The windshield stays pretty dry unless you trim her up too far in the slop and she falls into the next wave. Keep her nose down and you'll never stuff the bow. Some pics off Sebastian from the Long Point gathering:

http://i655.photobucket.com/albums/u...ps132bf375.jpg

http://i655.photobucket.com/albums/u...psc3296272.jpg

http://www.classicseacraft.com/commu...1&d=1367538969

I got to see the 25 Seafari on the ramp. Really interesting. Sick deadrise. I can see why she lands so softly. Very steep all the way up.

The 21 is really steep on the pointy end as well but she blends back a bit more to her stern.
The steps are also higher, which may help with surface tension.

I think that is the secret of the 21. And she is really deep.

Really.

A couple of things...:D

At one time Mr. Moesly once said, a bigger boat will normally ride better than a small boat.

The 25 was designed after the 21, so there should be some improvements build in.

Really the 21 was designed to go racing, and punching through head seas was important and getting wet was not.

The other thing I noticed from the pictures and I think Sandy and Denny can attest to it...Blue Heron and I think Connor are always standing up when they are punching thru the waves. On the 21 when I was driving and when Sandy was driving we never felt the need to stand.

Last of all this information below comes from a guy who has tested the 25 and 21 very throughly.

Quote:

Cleaning up my home messages and wasn't sure if I answered you. The boat is up and running and we have ventilation problems with the outboards that Jamie positioned somewhat between the keel and mid hull panels. Next week we're modifying the outboard bracket to move the engines furthr apart like I've seen on some of the old photos. We think if we clear the riser between the keel and mid hull panels we will see cleaner water. To counter the weight of the Armstrong bracket and twin Suzuki 140s, we've had to put 500 pounds of chain in the bow to get her to balance right. She runs great in a head sea, plunges a little too much to my liking in a following sea. Overall, very good forebody but not as good as the SeaCraft 25'. It probably could use more flare in the bow and a big spray rail forward between the chine and keel. What realy surprised me is how softly she landed when launching off 3' foot chop on top of 4' long swells. Considering the average deadrise is about 20 degrees compared to the 26 degrees of the SeaCraft 25', she is almost as soft!

The 21' is quite impressive and with the mods we've made to the 25', including a production 30' based on a geosim of it, it is obvious Moesly was a great designer. We are working on a high seakeeping 24-26' RIB with high displacement of ~ 8500 lbs. Based on our tests on the 25', she simply tops out at a displacement of 7500 lbs so it does not make a good parent craft. I was thinking of stretching the 21' to about 24.5' and was curious about the differences between the 21' and the Potter 23'. I have limited experience from riding the 23' over 30 years ago and as best I remember it wasn't that impressed with the ride and remember getting soaked. I need to know more about the 23' to see if stretching the 21' will detract from her seakeeping.

We have used a digital camera and 3d software to create a very accurate solid model of the 21 and 25 and the differences/similarities are amazing. If you keep the keel panel of the 21' as the baseline parallel to the static waterline, the mid and outer panels slope down as they move aft, about 1.5" over 6'.

Anyway, didn't mean to go on so long BTW, the serial # of my 21' is 111.

The old 19's are also the same way as the old 21's. No reverse chine. Looks like it would slice thru the water. Spray rails are gonna be a must.

Terry, thanks for sharing those comments. I had not seen that info, great stuff.

I think it was you first posted the comparison of the lines of the 21 and 25. Looking at that, the idea of stretching a 21 (I'd make the bow more like the 25) sounded like a great idea. Too bad I don't have the dinero.

On standing vs sitting, at least for me, its more a function of how well I want to see. I usually stand up for transition times and when I need to see real well. Maybe one addition to that. When crossing a steep wake at a sharp angle, its a lot easier to control the boats lean if I'm standing up. The boat's head sea ride is fine sitting, at least up to a Gulf Stream 4 ft at 20 knots.

Connor, I wish I would have gotten out offshore in your boat to feel some comparison on how my 23 rides compared to the 25 in similar seas on the GOM. I am really starting the the thought process on how I could modify a 25 to match the layout I currently have and whether the benefit would be worth the expense and time. What are your thoughts on comparitive sea handling between the two?

X2

Given what we were in early in the day, the 25 would run about 2 knots faster with more comfort. It lands much softer if it launches off a wave. Running to the last spot, I was sitting down in the back, so could not see the seas enough to have a valid opinion. Even all the way in the stern, every once in a while there as a modest slam. I don't think the 25 would do that. Given what I've been in before, 18 knots with slightly more comfort and far less hard slams is probably close for those conditions.

I've only run straight into a solid 5 ft once, just for rank curiosity and not for very long. Gulf Stream, wind had been blowing steady for 3 or 4 days, 15-18 knots out of the SSE. We were coming home from Bimini and I turned around a couple of times to run with boats going to Bimini. In the 5 fters, I had to slow down to 18 knots and stand up when I turned into it. To do it very long, 16 or 17 knots would have been more reasonable. Pretty much, the boat was staying in the water. For comparison,I was running along side a 30 something Contender type open fish. All his passengers were standing in the stern, the boat was jumping all the way out of the water about every 3rd wave. They did not look happy. I think he was going a bit faster than me, but not much.

The 25 rolls more than yours, less of a problem for divers than drift fishermen, but still an issue. I think monster tabs would tame it down a lot.

I think you would have a hard time matching your bowling alley in a modified 25. To keep a windshield and move the helm forward , it gets narrow pretty quick. Also,I suspect the 25 doesn't have the weight carrying ability of yours. Get a hold of bigfluke, he is the real expert, especially on that sort of thing.

If you would like to come down on a snotty day(After new year), I'll be glad to provide a ride. You will love driving her. She really responds to a good helmsman.

Couple of additions

If you slow down to 15 knots or so, the boat should stay in the water and be comfortable running into darn near anything.

Its following sea performance is as outstanding as in a head sea. The boat loves to surf in quartering or beam sea. Surfing in big beam seas is a hoot.

In one way, the boat is funny, different from anything else I've run. I've been out a couple of times in it when I shouldn't have. Look around the boat and your hair would stand straight up, but the boat always felt totally confident, in control and solid. Far as it was concerned it was always just a walk in the park. The juxtaposition of what it looked like and what it felt like was odd as heck. I did not trust it for a while, just too odd, but I'm beginning to.

Seafari25 would be another very good source of information.

I was on Dave`s boat at Sebastian. Sitting comfortably. We were runnin` with Conner when the "photo" was taken. At least 6 ft. of air under his boat. At least! The ride is mind blowing.

I`ve also been on Chuckle`s 23. The ride is amazing compared to my 20 sf, but it is not really fair to compare it to the 25. The 25 is a whole other animal altogether.

When Dave came to look at the 25 race boat, he said the Seafari was steeper. Well, that raised an eyebrow. When Conner pulled his Seafari on Sunday, the first thing I looked at was the transom. Damn Son! Holy deadrise. Looking at the entry is a bit tougher. I couldn`t say which is steeper. Both are really extreme. I forgot to sight the chine to keel longitudinally.
Both have a fair bit of rocker in them as well. This is something that gets little discussion.
Look at the rocker on a Formula.

Denny has said many times that the 21 was the lead boat for rough water crossings to the Bahamas. 23`s followed.

Cheers,
GFS

She does land amazing soft, and that lack of slam makes a huge difference in how tired you get if running a long way. Jumping around is one thing, slamming is another.

I had her even higher than Sebastian once, props were part way out of the water and I was afraid of losing some teeth once we came down. Could not believe it when there was no slam.

Note: consistantly landing soft requires a good boat handler.

one more food for thought if you are planning a modification to an outboard.

Vertical center of gravity is real important in this hull. As built, it rolls, but does not snap roll. Add a hard top and twin outboards(I know someone who did this) and it has a truly wild, snap roll . Memory is failing, but there is a twin outboard model near running condition on the forum. I'll be real interested to see if it snap rolls.

Still.

So much to learn.
I surf up wakes and down with a boat. I roll in and fly the lip.

Some things are still fun.

My point exactly...a function of how well you want to see. I never feel the need to stand except when docking...

The 25 was Moesly's last design before he sold the company to Potter, so it's the latest evolution of the VDH design. I believe it was preceded by the 27' Seamaster, and I've noticed that the middle panels on both of these hulls flare out to a conventional lifting strake or "chine" about 2" wide up forward at the vertical step between the middle and outer panels. This strake disappears back about amidships, so I think Moesly added it to create a drier ride, just like he added the ~1" wide flat at the chine up forward when he modified the 19' Bowrider mold to create the 20. This flat also disappears about amidships. I don't remember if the 27 and 25 also have this conventional lifting strake at the step between the center and inner panels, but I suspect that Carl had learned by the time he designed the 27 and 25 that the deadrise up front was so high that a narrow flat spray deflecting strake up forward didn't significantly affect the ride, provided it disappeared by the time most of the hull was in the water at amidships.

The spray on Blue Heron's 25 pictures looks like it's being deflected horizontally by a flat strake, while the water coming off the inner and center panels on my 20 in the picture below, which has no strakes ala the 21, is simply following the angle of the inner panels. It depends on the outer panels and flat at the outer chine to knock down the spray, and the spray at the outer chine does look like it's being thrown out flatter than it is on the inner panels. My experience with the 20 is that if you get wet, it's because you're going too slow! It seems to depend on the flatter outer panels being high enough out of the water to deflect the water coming off the inner panel. It definitely rides drier than the 21 (but not as softly!) and it's wetter than the 25. The 21 has no flats anywhere, and as Terry said, it was designed to be raced and staying dry was not a consideration! Carl said that he intentionally designed it for very little dynamic lift, which I interpret as no lifting strakes and minimal flare in the bow. He wanted it to slice through the waves instead of lifting over them.

I think the more sloping bow on the 20 and 25 may also be responsible for their excellent handling in following seas, because as you run into the back side of a wave, the displacement and resulting lift as the bow is immersed would not increase as abrubtly it does in the 21 and 19 hulls that have a more vertical stem and less flare.

BTW, Carl loved that shot of my 20 when he saw it, and said they had spent HOURS at Lake X back in the early 60's trying to get a shot like that of the 21!

No question that the shorter bow of the 21 provides better visibility of the water ahead, and that's a good thing. I could probably achieve the same visibility if I stuck a fly bridge on my 25, but it would further screw up an already tender roll axis. All boats are a compromise. Ya pays yer money and ya takes yer choice. Your boat, Terry, is a sweet ride, and for what you plan to use it for, it's looks like it's ideal.

The 25 Seafari was Carl's design, but Potter built it. When I spoke to Carl about it he felt like Potter hadn't done enough testing before he went into production. Remember that Carl designed a dynamic ballast tank for his very deep vee designs, but Potter didn't implement it.

The touchy handling, and sensitivity to weight distribution of the 25 Seafari are ample evidence that it's not the right boat for just anyone. As has been said here before, it's a driver's boat. It actually handles more easily in 3'-5' slop than it does in a 1' chop with a cross wind. With 6 people aboard on the way out to Anclote last Saturday, I had some difficulty keeping mine from leaning to one side or the other. I don't know that the passengers noticed, but I did. On the other hand, put her in the slop, and a simple flick of the wheel lets you set up the right entry angle for the next wave. Lightly loaded, it's a nice boat whatever the conditions. But in the big stuff, she really shines whatever the load.

Great discussion going on here.

I fished on a 29 SeaVee based outta Jupiter. "Mumbo Jumbo". 330 Cummins IB. Capt. Scotty loved surfing the following sea on the incoming tide. His wife would look at me as if to say,
yes he is crazy and still the surfer dude of his youth. He would drop in like the hull was a surfboard. I knew it was a diesel, but always worried about losing power. I do this on wakes, but not in a cut like Jupiter.

The 25 blows the 29 SV away in a following sea. She just greyhounds over their backs without a feeling of getting caught in the mush. That was most impressive. This goes back to how fast can you run in my mind. When you can get on top and run, you miss the valley.

I`ve experienced this while bump skiing. Dust the tops and you dance. Stay in the line that most take and your ass will remind you it is your biggest muscle.

For us right now the 21 is the Deal...however that being said. If Sharon and I went back to the boat camping hanging on the hook thing again, I would be looking for a 25. No comparison but as I stated before to you guys we really liked our 24 Searay, which we bought new in 78. Very similar layout and we use to spend 2 weeks on it, with a kid and a dog.

Attachment 5796

Bushwacker has great analysis, as usual. I had not noticed the spray effect of the flat area forward on the inside strake(always wondered why that was there). When the waves are low, it is catching the spray and thats what makes the spray exit so far aft. When the waves get bigger, the chine catches the spay, same effect. Amazing that such small things can make so much difference.


Sandy, I spent several (calm) days diving out of that model SeeVee. Heck of a boat.
Did you ride on it enough to know what it feels like coming down after going airborne?

I don't remember the SV slamming. Just a solid hull with that Cummins in her belly.

Now I was on a Jupiter 31 once. It slammed and shuddered like a wet dog. The owner was no helmsman. Felt sorry for that poor hull.