Help picking a used jack plate.

[NWolf]

So it looks like my little 17ft bass boat has a bit of hook to it. That explains why I have to have the motor all the way down, and trimmed all the way up to cary the bow. I was looking at going with a 10inch jack plate to get some leverage. I have found several 12 inch plates for around $200. Will the extra 2 inches be a problem? It has a 6 inch plate on it now.

[nitro_rat]

Pics? Can you hold a straight edge up to the bottom and get a good side shot? Does that hull have a pad?

No jack plate is going to compensate for a bad hull...

[NWolf]

Yes it has a pad. Im not planning on fixing this hull. Its not worth it. Just gonna get it back for better leverage.

[nitro_rat]

This is from a quick search on straightening out a pad. This is the 3 hour fix. I bet it’s cheaper than a 12” jack plate...


the easiest way i found, was to use a 6 foot level, covered neatly in packaging tape (epoxy won't stick to it at all), and after cleaning and roughing the surface with about 60 grit, and wetting out the surface, thicken up your epoxy (not polyester in my estimation) with colloidal silica/cabosil and spread it on the edges of the surface. then lay your level on these areas from transom toward the bow. i do it on the edges of the pad, each side. then, once hardened, the levels will pop right off with zero effort and each side of the pad will be like glass in smoothness. then you can use the edges of the pad as a guide, and put your filler into the center of pad and use edges as guide. just smooth the center with a straight edge that hits the left side and right side of padthat are already done. the center will then be excellent. then once hardened, rough up and spot as needed.

does that make sense? really hard to explain without picture. if the filler is going to be 1/4 inch or more, or even close to 1/4 inch in thickness, i would mix some milled fibers to keep it from getting too brittle.

i actually did one boat like this without pulling it off the trailer. it was a 15 footer with a very untrue pad. i didn't want to remove windshield and seats, and motor, so i just got under the pad with the tools and did it. the only problem was the trailer axle was a pain to work around. but it was a total of 3 hour job, start to finish. by the way, once it is all finished, i would roll on a few coats of neat epoxy to the surface as a barrier, especially if boat will be left in water for days at a time.

[71V153]

Well that and ya ain't gonna fix a hook with a jackplate. Or vice versa ...

[Gordon02]

I would try a set of these blocks before buying a new plate. 12" is serious stuff and adds a lot to the stresses placed on your transom - at rest, trailering, and under way. These 2" blocks fit between the plate and your outboard, they are easy to install, and are cheap. I have had a set of 2" blocks installed between my Allison's plate and Merc SS. Available on eBay - Gordon

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[Gordon02]

NWolf, I've owned two different brand-new Astro boats and I'm currently doing a full restore/rebuild of a 1971 Astroglass 15 for a neighbor (predecessor/parent to the Astro). These are heavy and have lots of resin/glass in the keel and pad area - not something that would normally bend or distort.
If the pad has been properly supported by flat (horizontal) 2x6 bunks on each side of the pad - then the hook may be there by design. I've only seen a hull "hook" when improperly supported by the pad itself when stored on a flat surface. That was a flat bottom and was not build as heavy as the Astros. Photos, please - we all can learn something.

[NWolf]

I will add pics as soon as I can get them. I do think its by design though, because its even across the hole bottom, keel included. That said, I still have to be at full positive trim with the jack plate buried to run its fastest. I feel like Im loosing a lot of speed by having to trim so high. I think if I could get the motor back and get better leverage, It could gain quite a bit. Plus having the motor down so far actually makes it take longer to plane out.

[Gordon02]

Trim not only affects the boat's angle of attack and wetted surface, the gearcase itself doesn't feed water into the prop as it was designed when trimmed up past "straight ahead". The shape promotes laminar flow to the blades and allows the propeller to efficiently convert rotational energy into thrust. This shape/design works well up to the approx 80 mph mark going straight. Over-trim angle screws-up all that laminar flow science stuff with turbulence and leaves the propeller with "dirty water and gas" - water that is turbulent is full of air and will not hold the blades. Besides the fact that the propeller can't be efficient in generating thrust - the gearcase doesn't want to be pushed forward in the water. Have a look at these drawings and you'll have even more reason not to hit that trim button - Gordon

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[NWolf]

You dont have to tell me. Thats why Im asking about the big set back jack plate. Even though 2 inches might help, there's no way its enough toncorrect how bad mine is right now.

[FMP]

So if your slight trim ends up getting the bow to carry and the case end up close to level are you traveling or fighting for that balance? If it turns into mph then good.

[NWolf]

Huh? I dont have "slight trim". The higher I trim, the faster it goes. I have my jack plate all the way down so that the prop stays in the water all the way to full up.

[NWolf]

And after looking at the hull in better light today, its not hooked at all. What Im seeing is the way the pad comes down from the hull at an angle, getting taller as it comes back.

[FMP]

When running and the hull is lifting out, the trimmed case works fastest if it can level itself negating the trimmed angle. Hence little or no rooster

[Glasstream15]

It sounds to me like you have the wrong prop. More info on that please.

[NWolf]

I dont know where you got that from what you read. I never said what speed, rpm, hole shot nothing. But it is a 24 pitch raker spinning at 5500 and the hole shot is fine. The rpm would be higher if I didnt have to trim to the moon. And it does this with all 4 props that I have for this boat, always has. Did the same thing with the two motors that were on it before.

[Gordon02]

NWolf, I've got some articles that I wrote for Bass & Walleye Boats magazine years ago (mag is long gone) that details the stresses and loads jackplates place on boats and the bolt clamp loads for different fastener materials. I'm working on getting them posted up on my website for public service - I should have that work done next week.

A few questions for you to get to the bottom of the problem quickly with one trip to the lake on a quiet day.
1) Do you have a trolling motor on the bow that you can temporarily remove?
2) What gear, extra batteries, parts, storage items do you have in the boat that you can safely leave at home?

Here is why I ask ....... Assume the fulcrum of your boat (exact balance point) is say 2 feet forward of the transom. Any weight you can remove has the following affect-
A) 1 foot forward of that fulcrum, weight is 1:1 in leverage pushing downward (your hull and outboard must over-come and lift).
B) 10 feet forward of that fulcrum, weight is 10:1 in leverage pushing downward (30 lbs of gear in the forward locker is equal to 300 lbs pushing downward at 10 feet!
c) That 70 pound trolling motor 15 feet forward of the fulcrum...Yep 15:1 or 1,050 lbs in leverage pushing downward!

Now you can go to the lake and see what's going on. You should be able to run neutral and fly that bow! Be prepared to watch the water pressure gauge and start raising the jack 1/2" at the time until you lose pressure or can't carry the bow.

It's easy to see how and why weight forward of the fulcrum is a bad thing (increases wetted surface area). I run an old OMC Sneaker 12V trolling motor that weighs 55 lbs on the end of a 20' Allison XB2002. Removing just the troller up front, extra gear, and the Group 31 battery makes a HUGE difference in bow lift. I can immediately raise my outboard another 1" (would be 1.5" above the pad), run a 30 Chopper II on the limiter at 6,750 rpm, and barely touch the trim above "4" (4 is neutral on my boat using a 100% manual cable trim indicator). The boat flies and trim is carefully administered without the weight.

Hope we're helping. Wear that Lifeline safety vest and look out for logs.....Gordon

[NWolf]

I did remove everything from the forward compartments this last weekend and it didnt have any noticable effect on lift. Meaning I still had to trim full up. As for the trolling motor, its not really an option. I fish tournaments and wouldn't run without it anyway so it wouldnt matter to me how it runs without it. As far as the stress on the boat is concerned, the real stress on the transom comes from thrust not the weight of the motor like so many people like to say. So my motor being as low as it can be is actually putting more stress on the top bolts than it would be if I could raise it up. So if I can get it back farther and rais it up the two should nearly cancel each other out. I know 12 inches is extreme, but its all I can find.

[NWolf]

Gordon, I hope that I didnt come off wrong with that last post. You seem to know what you're talking about so I probably should have thrown in a question mark or two. But you see what I mean about the thrust right? The distance from the center of effort ( the prop) and the fulcrum (bottom bolts) is the real issue with transom stress. And so raising the motor reduces stress while set back increases it.

[Gordon02]

Yes, you've got the stress pegged correctly - specifically a 2" deflection of the trailer springs at 60 mph (1/88th of a second) generates only 870 lbs/ft of leverage force when using a 6" jack and 400 lbs outboard (yours weighs approx 360 lbs). At rest, I reported 600 lbs/ft of leverage force. The 150 horse outboard (your's has been modified) generates approx 1,356 lbs of thrust which calculates to 2,904 lbs/ft of leverage force at the transom with zero (0) setback. Your 6" jack calculates to 3,130 lbs/ft of leverage force. Just fyi - the 12" setback increases that to 3,616 lbs/ft.

Have you weighed your boat? Can you find a local scale that you can weigh the trailer loaded and empty for difference? There is also a formula for triangulation weighing - whereby you use scales to measure each tire and tongue to get both weights - loaded and empty. Gordon

[NWolf]

I haven't weighed it yet. I do think its heavy, but its not water logged. It doesn't have any foam in the bottom, just around the gunnels. And I drilled into a stringer a while back to check it. I think its just a tank.

[Gordon02]

My first new Astroglass was a 1986 166V fish/ski that I powered with a Johnson SPL88. As set-up by the dealer, I could get 43 mph. With careful set-up, jackplate, Raker prop, and water pressure gauge , I got that number to 48. My 2nd new Astroglass was a 1987 178V single console bassboat that I powered with a Johnson GT150 bass engine (cross-flow). As set-up by the dealer, 62 was the best it would run. Again, with careful set-up, 6" jackplate, 24" Raker, and a water pressure gauge - 68 mph was my best result. I could never match my friend's Venture numbers of 71 mph nor his brother's Norris Craft/Mercury XR4's numbers of 74 - These Astroglass boats are heavy - theirs were not.

[nitro_rat]

I was reading somewhere that those Astros are 9 layers of heavy glass with no core. Yep, built like a tank!

[FMP]

Good read

[NWolf]

Im actually glad that its built that way. Ive put it high and dry on submerged stumps twice now. No damage at all. I was just over idle both times, but the entire boat was being held by one square foot. So gordon, a 10 inch then should be max? Take what it gives me and call it good? The speed isnt my main concern just so you know. Having that motor so far down means that when Im at full negative trim the prop shaft is pointed at the front of the boat instead of the back. So it actually has a harder time climbing up, and it doesnt like to cruise slow. With the jackplate up a couple inches it jumps right up and will cruise along at 25 no problem. Of course it wont go over 50 set that high either, so thats a no go.

[Gordon02]

NW, I've never needed that much set-back for a standard configured boat/motor set-up. A 6" jackplate has been plenty for more than a dozen boats I've owned and helped close friends with. Only with my 178V/GT150 did I go with additional 2" blocks something like those I linked above. With 8" of jackplate/blocks, I was able to carry the bow even where I'd run out of water pressure.

What offset does your boat have? Some boats don't have any and others a bunch. If yours is one that doesn't, then the 10" you're proposing isn't that much. If you've got good offset, then the factory has some of your jackplate "built-in".

I run a propshaft height of 1/2" above the pad with a short-shaft Merc SS (15" model) so I had to replace foot leverage with set-back leverage to carry the bow. Even with my 20 footer, I only have 11.5" of total jackplate/blocks with a factory transom offset of 6" built into the hull. At neutral trim, there are 33 inches between my pad and propeller. That's quite a bit of leverage. I am not understanding why yours would need all of that unless you don't have offset.
What about your lifting strakes beside the hull? The chines of most boats are hooked sharply downward at the rear to promote quick planing and reduce porpoising (bow down effect) - perhaps the strakes beside the pad have some of this hook on purpose. If those are still in contact at full speed - they are killing bow lift. This would get back to weight in the boat.

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[NWolf]

The front of the boat is empty the back still has stuff in it, but its less than 50lbs of extra stuff. Batteries and fuel aren't extra. The pad is actually what angles down on mine. And its not at the back, its the whole thing. The center 1.5 foot of hull seperates from the hull at about a 1 degree angle from 4 feet forward to a height of about 3/4 of an inch at the stern. So if you look down the keel, it looks like it dips at 4 feet up. I took pics but you cant really see it on there.

[NWolf]

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Just like this! except mine does'nt have all those strakes, and is still a vee. Ok, maybee not just like this. This one looks like it comes up then is level. mine is a wedge from start to finish.

[Gordon02]

NW, the boat in the photo looks fine. It does not look like a particularly fast design, but the pad is not "hooked" from what I can see. I see where the pad starts several feet forward of the transom, but it's got plenty of surface to support the boat - the idea is that forward of that, the entire boat will be free and out of the water. I'm more in favor of having a better defined pad that has pronounced distance between the center pad and the lifting strakes beside it. This yellow hull has an extra-wide pad that incorporates the first set of strakes to help support / "ski" the boat at speed. This means the yellow boat will have more wetted surface than a boat design that has a single, flat pad. The sharp vertical edges of the pads edges and each chine are meant to shed/shear water so as to "break" the surface bond and reduce drag. In this one, they have long vertical surfaces that do nothing to promote lift yet must stay wet to provide weight carrying surface of the pad.

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[nitro_rat]

I was looking on some bass forums and 50 mph seems to be about the norm for the 17 astros with 115-120hp, some with bigger power we’re claiming up to 62 mph. Most of these numbers are probably optimistic pitot tube speedo numbers so you may not be far off the norm performance wise for the hull.

My 17’ bass rig will kite the bow at any speed with excessive trim and that’s with the trolling motor and battery mounted forward. The PO mounted the trolling battery in the forward livewell and I’ve been too lazy to change it. I’m running an old 175 but it’s powerhead rated so probably closer to 150hp at the prop. I can jump out of the water prop and all at high trim with a 24 or lower pitch prop. 75 mph gps no problem with a 27 SRX, still has good hole shot. Some of your performance issues may just be hull weight/design related.

[NWolf]

Mine does more than 50. 55 is the best so far, but I had a clogged high speed jet when I did that and the jack plate was still up to far. I have the carbs all cleaned out again (second time it happened in twoo weeks) and all fuel lines replaced. Should be around 58 this next time out.

[FMP]

You're optimistic about a heavy hull as you claim making that speed with a 120.

[NWolf]

Its not a 120 any more. And those are gps speeds with the timing still set at 14 degrees for the break in. I have video of it on here showing the tack and the gps doing 50 with an 18 pitch when it was set at 10 degrees. Now it spins a 24 raker. Ill post another video of it when we turn it up this week. But again, this post doesnt have anything to do with any of that. It is because it doesnt want to cary the bow with the 6 inch plate. Maybe when I turn it up that extra speed will make the difference in lift, but I doubt it.

[FMP]

How's the top 1/3 of your transom, good enough for the extra outward rear force? Knees?
Same style?
Kind of like when I have a long handled spade shovel firmly planted under a root and pull down with a bit too much force and bust the handle at the base. Damm leverage

[Motv18]

It should get close to 60. Astros can run. Depends on water logging and gear.

I honestly would need a stern transom pic, some have built in set back.

That at may be the cause the slip