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88 Spectra 171 Jack Plate Info

V

VLP

Member
I just picked up an 88 Spectra 171. Has the factory Merc 150 XR4 Motor on it mounted directly to the transom. From what little information I have found on these boats, it seems that adding a Jack Plate of some sort is common practice due to the weight of the Spectra's bow. I would like to know if anyone has any suggestions as to what size to run and what to look out for. I can get a CMC manual jack plate locally for cheap, with a 5.5" set back. Are there any drawbacks to using a jack plate? and would this set back along with the 5" adjustability provide an increase in performance? What else is affected positively by using a jack plate?
Thank you for all of the info in advance. You all have been very helpful so far!
 
Jackplate will likely help holeshot, chinewalk and top speed. You will be able to run the motor up and back thus lifting the boat out of the water.

I just put one on my boat and makes a world of difference. Check your cables and motor mounts.
 
My first Checkmate was a Spectra 170 bowrider with a Mercury XR2 150. I never had the chance to run a jackplate on the boat but I'm sure it could've used at least 6-10" of setback. You will be able to gain more leverage to lift the boat out of the water and get cleaner water flow to the prop by using a jackplate. Get a hyd. jackplate if you can afford it. Than you can fine tune the plate while underway. I would go with 8-10" on a 17' hull. There was a guy on this site years ago who built a killer Spectra with big setback and power...not sure whatever happened to that boat. I think it was in North Carolina.
 
Awesome, that's what I was looking for is an idea of the set back. Thank you, I was unsure as to how to go about figuring that out. I assume that more setback = more strain on the transom, im a little concerned about that. Do people run transom savers or reinforcement when hanging a motor 10" or so back?? I have a Merc 235 sitting on my (cough) hydrostream (cough) lol But again it seems that no one really knows much about the Spectra so im unsure how well they hold big power. Keep the comments coming! thanks!
 
Anyone have anything bad to say about the Merc Paralift? 12" setback and hydraulic, one for sale locally for around the price of a manual plate new.
 
I would think you should keep it under 10" if its the original transom and knees. If they have been upgraded then go for the 12.
 
It is all original. Is there a large difference between a couple inches, say from a 5.5" to an 8" to a 10" and so on?
 
VLP said:
It is all original. Is there a large difference between a couple inches, say from a 5.5" to an 8" to a 10" and so on?
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It does make a difference the more you go back. The stress increased exponentially. You could reinforce your existing knees by doubling up the thickness and making sure they are bonded to the stringers, transom and topdeck. With the boat only being 17' I would stick to 10" or less.
 
Thinking about it I would do the 5.5 and see how it reacts. You can always add a relativel inexpensive set of Bob's brackets to it later to increase the set back.
 
That's kind of the plan I had in mind. From the sounds of it, 5.5" is still going to improve upon transom mounted.
 
When I added a 5.5" jack plate to my Pulse 171 (basically the same boat as your Spectra) I didn't notice any gain in top speed. Not really enough setback, but it does allow you to play with engine heights, so it's worth it. Also, your steering cables (if original) will keep you at only 6" setback anyway. Any more, and you'll have to change your cables to longer ones.
 
good to know. I will have to look into what all would be involved in the steering swap to longer ones. I see a lot of 8" and 9" jack plates going over at scream n fly. Another question I have is I see people saying things like 15" mid on 20" transom. What are they referring to? Im assuming these measurements are of some kind of concern when choosing a jack plate or at least for setup?
 
A 15" mid is basically a 'short shaft' or 'standard shaft' motor. Your boat has the 'Long shaft' 20" mid I assume, which your transom was designed for. XL motors mean 25" midsection, and XXL are 30" midsection motors.

The S&F hot rodders are putting 15" midsection motors on 20" transoms to get the lower unit up higher without raising the whole engine way up. If you have enough jack plate, you can mount a 15" short shaft (standard shaft) motor lower on a 20" transom for reduced center of gravity and reduced wind resistance while keeping the lower unit at an optimum height.
 
Okay, thank you for that explanation, that makes a lot of sense now. I was having a hard time trying to put it all together in my head. What are your thoughts on bracing the transom somehow? I know that stress cracks in the splash well corners are of concern for checkmates, I currently have none and would like to know how to reduce the stress as much as possible when adding a large setback jack plate. I know Jupiter touched on this point, but wondered if there was a "bolt on" approach to adding rigidity.
 
VLP said:
Okay, thank you for that explanation, that makes a lot of sense now. I was having a hard time trying to put it all together in my head. What are your thoughts on bracing the transom somehow? I know that stress cracks in the splash well corners are of concern for checkmates, I currently have none and would like to know how to reduce the stress as much as possible when adding a large setback jack plate. I know Jupiter touched on this point, but wondered if there was a "bolt on" approach to adding rigidity.
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The only bolt on approach is to have tie bars from the top motor mount bolts bolted to the stringers. This would involve drilling through your splashwell (and possibly floor to access the stringers) and bolting the tiebars to the stringers. The right way is to beef up the inside of the transom by strengthening the transom knees and bonding the transom knees, top deck and transom together to form a unitized structure. It sounds harder than it really is. It's one-two days of itchy, sticky work but worth the effort.
 
I hope it does sound harder than it is, because it sounds pretty hard! haha Have there been any "how to" guides of sorts posted on the topic on here with pictures and what not?
 
Just picked up a TH Marine 6" Manual Jack plate for a decent price, should arrive next week. Would reinforcement be necessary for running a 6" jack plate as opposed to an 8-12"?
 
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