My 1975 SeaCraft 25' Seafari rebuild thread

[flyingfrizzle]

Well while I wait for a good warm day to bond the core in with the thickened epoxy I decided to move forward with the build and get the outboard bracket built. I got some 3/4" melamine from home depo and started to figure out how I was going to build the bracket. I decide to make the flotation tub as large as possible so I can get as much flotation at rest as possible. With the deep vee on this hull I think I should be able to get a fair amount more out of it than the one I did on my 20'secptre. I will be going 60" wide which will take it out almost to the outer edges of the second or middle steeps on the hull. I am coming up 2" from the hull bottom to allow for the water rise and following the deadrise of the second panel. This is a 20 degree panel and will give me about a 40 degree vee on the bottom of the tub. I thought about following the steeps of the hull bottom and changing it from 20 to the 26.5 degree of the first panel but think I will keep it a constant grade across both panels. This will allow me 4" at the bottom of the vee so I can get two garboard drain plugs at the back of the transom with out having clearance problems with the tub. The variable deadrise would look cool on the bottom of the tub but would not work well with the drains and it dose not add much air space so it would be a lot of extra work for little gain. The set back will be 22". I want to keep it to a absolute minimum so it dose not kill the balance of the hull too bad. At 22" I hope to be able to tilt the motors up enough to clear for safe travel and for good clearance in shallow water if needed. If I cant obtain full tilt I will limit the tilt on the motors so it will never hit the top of the rear of the transom but with twins space out wide it might actual clear tilted all the way up.

[flyingfrizzle]

I have a question for the knowledgeable up here, I have some questions about setting up twins on the 25'. I know most people set twins up on 26"-28" centers, sometimes 24" center to center minimum - to 30" center to center is common. You see more set close together than you do apart but I have read up here and told by some of you guys that you will get the cleanest water for the props if you set the motors center of the center panels (middle hull steep). This would set the motors at 50" centers apart. I looked back at some pictures, and the early 21' race boats had motors spaced far apart with the little low power (55hp) homelites but most of the latter 21'race hulls had the (mercury 110hp) motors very close together. I am wandering if they found to have better performance running them close together. I know that people say the closer the more speed you gain and less blow out when turning. Most of the go fast guys run them close together as possible for several reasons but know the vdr may behave differently. The turning may be the biggest issue with the wide spread due to the 25' rolls so much, I would think it could cause a bad blow out issue on this hull. Also I have heard that too close together may cause water to be stole from prop to prop and counters could cavitate if too close. The engine height will vary depending a pond where I place them, and far as now I figured on setting the bracket mounting tab at 31" above the hull bottom so that it would take a single 30" leg motor with the AV plate slightly above the keel. So with me running twins (25"legs) that would work out if I did the 28" centers but if I run them out apart further the mounting tab would need to rase the motors an additional 3" or so to compensate for the deadrise. You don't see many outboards today spread apart far except for cat hulls and such so I am guessing there is a reason. Also one other question, How much toe in do the motors need? I have read that at the standard 28" apart they need 1/4" of tow in for counter rotators. If spread further apart would this change? What would work best 1/8" or 1/4" or? I assume there is a lot of trial and error here but like to have a good starting point. Bushwacker, and any of you other engineers or experienced guys in performance twin set up help!

Here is a few pic's to show the spacing on the twin outboards on the 21' race hulls which as very very similar contour to the bottom of the 25's as shown by another member before up here that graphed the bottoms on a cad computer program and compared them.


These two are close together:





These two are further apart:

[Blue_Heron]

You bought your boat from George, right? Didn't it have twin I/Os? How far apart were they?

That being said, the original spacing may or may not have been ideal. I think your thought process on the pros and cons of wide versus narrow is good. As you said, the boat heels a lot in a turn, and that may cause the outer prop to blow out in a sharp turn. On the other hand, with outboards you have the flexibility to adjust engine height to compensate.

The best guy to ask would probably be bilgerat. He's got the only 25 I've seen with twins on a bracket. If he doesn't respond here, you should consider sending him a PM.

Dave

[flyingfrizzle]

Originally Posted by Blue_Heron

You bought your boat from George, right? Didn't it have twin I/Os? How far apart were they?

That being said, the original spacing may or may not have been ideal. I think your thought process on the pros and cons of wide versus narrow is good. As you said, the boat heels a lot in a turn, and that may cause the outer prop to blow out in a sharp turn. On the other hand, with outboards you have the flexibility to adjust engine height to compensate.

The best guy to ask would probably be bilgerat. He's got the only 25 I've seen with twins on a bracket. If he doesn't respond here, you should consider sending him a PM.

Dave

Thanks for the imput, True, I didn't think about the dimensions of the twin outdrives. They appear the be as close together as the motors would allow. I think there may be some clean water to be had in different spots off the vdh but after reading for hours I have a good idea what works best for most boats so I know where to start. There is also a fellow north of me in Virginia that has 76 25' with twin v6 mercurys on a bracket and I have spent some time talking to him over the phone. I would like to reach out to bilgerat if you read this give me a shout.

[Bushwacker]

Originally Posted by flyingfrizzle

I have a question for the knowledgeable up here, I have some questions about setting up twins on the 25' . . . Bushwacker, and any of you other engineers or experienced guys in performance twin set up help!

Friz,

If closely spaced motors see much air from that inner step on the VDH, they may be just as likely to blow out or might have to be trimmed down lower than if they were mounted further outboard! However I only know enough theory to be dangerous, and have absolutely no experience with twins and so I respectfully defer to bilgerat, and especially Fr. Frank, who has lots of experience rigging and running twins on very deep narrow hulls. Forum member Flying Time is a naval architect who also owns a race boat hull that's similar to your 25 and may also have some good advice.

I'd also suggest you send a PM to Carla (65Bowrider) to see if she can ask her dad what he'd recommend for a 25 Seafari with a bracket. I know he recommended the wide spacing for their Moesly 21 project boat which originally raced with the twin Homelites, both for "clean water" and minimum draft considerations. He also commented that the twin 250's on the bracketed 27' Seamaster "Sea Mistress" he bought were mounted too close together. Both of those boats have less transom deadrise than the 25 however, which may be a totally different animal. At the transom, GFS's race boat hull looks a lot like the 25 Seafari without the outer panels, so whatever worked best on the narrow race boat hulls might also apply to the 25. You probably have the motors mounted close together on your race boat, so that gives you a test vehicle that you could use to experiment with toe-in/out, etc. I'm sure that the Merc folks probably did lots of testing at Lake X on the race boats to determine what combinations gave the highest WOT speed. On a family cruising boat however, other factors like draft, handling characteristics, fuel efficiency, and low speed planing ability are more important than a couple of mph in WOT speed, and that might be why Carl recommended the wide spacing!

[flyingfrizzle]

Well I have most of my bracket mold cut and assembled. I used 3/4" Melamine sheets to form the mold so that I could wax the surface and have few to no sticking issues. I sometimes use MDF sheeting and then line it with plain white Formica which works better for doing curved parts. I decided to make it 22" high to the top of the swim platform with a 22" set back. Not a 100% sure the motors will get a full tilt here but if they don't I will modify the rams so they will not over extend and hit. I am much more concerned with minimizing set back vs getting more tilt. If I can tilt the motors up enough to get past the hull bottom and also clear the road when on the trailer then that will be all I need. Just want to help the balance by keeping the setback short as possible with out notching the transom and loosing the factory fish boxes across the back. The flotation tank will be 60" wide to go all the way out to the start of the 3rd steps. That will leave me just enough room for trim tabs or k planes. The swim platform will be 72" wide extending 6" past each end of the floatation tub. The flotation tub will be mounted low as possible, at 2" up from the hull bottom to clear the rise of the water rolling off the back of the transom. The tub will also have a 20 degree vee on the bottom to match the second step deadrise so that it will parallel with them. This will leave just enough room under the bottom of the tub for a garboard plug set center of the transom. The vee section of the tub will be angled slightly upwards to the rear point to allow an additional 2" of clearance for the water surface. This should be enough to keep the flotation bracket from dragging the water when the boat is running with no trim.
It was fun figuring out all the angles when cutting the pieces and designing the bracket. The transom in the 25' seafari is about 12.5-13 degress just like some of the other seacraft hulls. With the transom lay back and the upwards taper of the flotation tub aft made for some complicated compound angled pieces that were a little brain racking to figure out but not so bad once it was plotted out on paper.
I made the sides of the tub section of the mold taller than needed so that when I glassed it in the top edges would not roll away from the side of the mold when the fibers curl out past the top edges. I will just cut it to height with a thin cut off wheel once popped out. The front side that will bolt to the boat will have a 4.5" notched lip inwards to allow for the swim platform front lip to lap over it and in place while maintaining a flush surface. I actually cut the last 4.5" off of the front side of the mold then used a 1/4" piece of ABS plastic to space the top strip inwards towards the rear of the mold then backed it with some scrap 3/4" ply that was scrap from the transom core. I also added a 6" wide strip of 3/4" ply to the top of the front of the mold just to hold it square. In the pics below you can see the stepped section. I will contour the corners tonight with clay and round them with my radius forming tools. Then it will be ready for waxing and layup.

Here is a few Pic's:

Cut and ready to screw together:





Attached together:





Showing the notched edge for the overlap of the swim platform:







The sketch and design...lol

[Bushwacker]

Originally Posted by flyingfrizzle

, , , The swim platform will be 72" wide extending 6" past each end of the floatation tub. The flotation tub will be mounted low as possible, at 2" up from the hull bottom to clear the rise of the water rolling off the back of the transom. The tub will also have a 20 degree vee on the bottom to match the second step deadrise so that it will parallel with them. This will leave just enough room under the bottom of the tub for a garboard plug set center of the transom. The vee section of the tub will be angled slightly upwards to the rear point to allow an additional 2" of clearance for the water surface. This should be enough to keep the flotation bracket from dragging the water when the boat is running with no trim . . .

Good idea on minimizing setback and making a wide tub!

On the width of swim platform, you might want to consider extending it far enough past flotation tub to be able to mount a swim ladder underneath platform! Regarding angling bottom of swim platform, you're losing some flotation doing that. Looks like you're planning to mount it a bit lower than mine to gain flotation (good), so understand desire to prevent dragging in water, but might want to send a PM to Don Herman about that. The Hermco bracket is straight on bottom and longer (30"), but it doesn't drag in water when on plane, even at 12 mph. Even if it did drag temporarily coming on plane, it would act like a trim tab and provide more stern lift to help boat get up on plane, so I don't think that's a bad thing! Might look at making bottom straight with no slope but mount about 4" up from bottom, and see which design has more flotation.

[flyingfrizzle]

Originally Posted by Bushwacker

Good idea on minimizing setback and making a wide tub!

On the width of swim platform, you might want to consider extending it far enough past flotation tub to be able to mount a swim ladder underneath platform! Regarding angling bottom of swim platform, you're losing some flotation doing that. Looks like you're planning to mount it a bit lower than mine to gain flotation (good), so understand desire to prevent dragging in water, but might want to send a PM to Don Herman about that. The Hermco bracket is straight on bottom and longer (30"), but it doesn't drag in water when on plane, even at 12 mph. Even if it did drag temporarily coming on plane, it would act like a trim tab and provide more stern lift to help boat get up on plane, so I don't think that's a bad thing! Might look at making bottom straight with no slope but mount about 4" up from bottom, and see which design has more flotation.

Thanks for the insight, I can make the swim platform wider for the ladder to fit under and that might be a nice addition for the kid getting in and out of the boat (this will be out family boat). How wide of a space is needed for a telescopic ladder like you have? I was going with the 72" wide unit due to that is what my last one was on the 20' hull and I already have the top half mold built. I wanted to make it 84" wide but after looking at the rear of the boat the 72" would give me clearance for the rams for the trim tabs or the K planes that I will probably use. I have the tub so wide and the swim platform so low it doesn't leave much room for the tabs rams. I want the platform low to the water as possible and even with the low clearance model tabs I don't think I have enough vertical room to mount the top of the ram. The narrower platform will let the rams mount beside the edges and clear the platform. I don't want to cut holes in them and run them threw the swim platform or I don't want to use the Volvo tabs (they are nice but not good for my application). I have a sketch of a custom trim tab I will build if I do not get the expensive K planes that is similar to Mr BlueHerons tabs. It looks like I go with have to go with the more narrow platform and have room for the rams or I will have to make some kind of low mounting custom rams for the tabs that will mount low enough to clear if I make the platform wider. I don't mind making a new mold for the top half, but just need to figure out the details so the ladder and tabs will all fit correctly or it will not be worth doing and then it will make more since to use the 72" mold I already have.
Now about the taper on the tub, I may be worried about something that will not be a problem. I figured it may need the extra room due to me mounting the tub so low. I didn't realize the Hermco is straight outward on the vee part of his, Every bracket that I have seen other than his has had a taper up wards on the vee and more than the 2" that I used. Most taper is like 4-5" up wards. I don't want to loose the volume and had it sketched out as a straight leg but after pulling strings and taking measurements I figured it would drag unless the boat is riding very flat, level or have the tabs buried to keep the nose down. Even with the 2" up wards angle it will only allow for a minimal attack angle before it drags. I changed this last minute after reading about another guy who made one without the taper on the vee and it caused his to porpoise back and forth he clames. He said it would hit the vee and then it would make the nose dive like a tab would but then it would lift back on it and start proposing. He said the boat did not do it before the bracket but only after installing. It was mounted low also. His may of just been a balance issue mainly but it got me worried and that is my basis for adding it.
Far as what would have more flotation volume (not a math wiz) but the 2" taper vs no taper at a 2" higher mounting height would cause me to loose more volume if mounted higher even with the straight leg? The lower 2" mounting would allow the larger part of the tub to sit in the water more vs only a 1/2 of the 2" slice I am cutting off. Correct me and I may be wrong but wouldn't the lower mounting with the 2" taper yeld more volume? You got me curious now because the main thing I wanted was the most volume as possible with out any negative effects. Looking at other pics of 25' seafari's they seem to ride bow proud with the hulls planning at an angle upwards and this would greatly effect the outcome of needing the angle cut on the tub or not I am thinking? I figured to start with the water rising off the transom will rise at 1" per foot back, so that will leave little clearance at 22" back due to the water should of rise around 2" at this point letting it just scrape by with out any addition room for error and that is assuming the boat is level in the water at plane. Factor in the angle of attack the boat will ride at and that will cause the tub vee to angle down into the rise of the water leaving the transom. I might be over thinking all this but that has been on of the blind factors I have been trying to figure out. Any more incite on this would be greatly appreciated.

[CoreyTrx]

I like your bracket design. I made my bracket just like the Hermco's with it straight back. It doesn't angle up. Mine is a 30" set back and mounted around 3.5-4" up and it doesn't drag. It has more then enough flotation also.

[Bushwacker]

Originally Posted by flyingfrizzle

Thanks for the insight, I can make the swim platform wider for the ladder to fit under and that might be a nice addition for the kid getting in and out of the boat (this will be out family boat). How wide of a space is needed for a telescopic ladder like you have? . . .

Now about the taper on the tub, I may be worried about something that will not be a problem. I figured it may need the extra room due to me mounting the tub so low. I didn't realize the Hermco is straight outward on the vee part of his, Every bracket that I have seen other than his has had a taper up wards on the vee and more than the 2" that I used. Most taper is like 4-5" up wards. I don't want to loose the volume and had it sketched out as a straight leg but after pulling strings and taking measurements I figured it would drag unless the boat is riding very flat, level or have the tabs buried to keep the nose down. Even with the 2" up wards angle it will only allow for a minimal attack angle before it drags. I changed this last minute after reading about another guy who made one without the taper on the vee and it caused his to porpoise back and forth he claims. He said it would hit the vee and then it would make the nose dive like a tab would but then it would lift back on it and start proposing. He said the boat did not do it before the bracket but only after installing. It was mounted low also. His may of just been a balance issue mainly but it got me worried and that is my basis for adding it.

You can buy ladders in various widths. The one I got was a Windline and needs 13" of width to install. It's a clever compact telescoping design, and works well when lowered, but the top section has to slide thru some U-shaped brackets lined with teflon so can be a bit difficult to raise and lower unless you remember to spray it down good with some silicone or super lube before you launch the boat! There may be other designs that are easier to deploy.

You should be able to lay out/compare the geometry of a flotation tub extending 30" straight back from the transom mounted about 4" above keel vs. one mounted 2" above keel and only extending back 24" to see which is closer to water. The angle/rise of water coming off transom will change depending on speed; more rise at low speed. That hull should plane at about 12 mph if it's balanced right. Maybe you could make up a piece of aluminum angle/plate to simulate dimensions of tub and try it out on your race boat to see if it's clear of water!

My experience is that porpoising occurs at higher speeds, 20 kts+. I think most boats will tend to porpoise after adding a bracket just due to the CG shift caused by moving the motor back, even if tub is clear of water, unless other stuff like console and gas tanks are shifted forward to offset the weight of motor moved aft.