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Why I do not like jackplates!
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ContinuousWave Whaler Moderated Discussion Areas
ContinuousWave: The Whaler GAM or General Area
Why I do not like jackplates!
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| Author | Topic: Why I do not like jackplates! |
| captbone |
posted 02-09-2003 06:06 PM ET (US)  
I have always been one to vote against jackplates for whalers. Some people love them and I do not. Everyone always asks why and tell them that it is more stress on the transom. Engineers and formulas have been give to prove me right and wrong. On www.classicmako.com (great site) I found a guy who had to rebuilt the transom because of what "I BELIEVE, MY OPINION" to be a jackplate related failure. Check it and tell me what you think. |
| jimh |
posted 02-09-2003 10:19 PM ET (US)
Actually, there is not an election to decide if jack plates are suitable for use on Whalers. Everyone decides for themselves. You are welcome to vote against them, and in your case you will always win 1-0. |
| captbone |
posted 02-09-2003 11:20 PM ET (US)
This is not a vote! I just want to see what other people think. I am going to believe what I want, but I always consider other opinions in making up my mind. |
| Bigshot |
posted 02-10-2003 10:37 AM ET (US)
I think you need to do more research than one man's account on a Mako site. Do jackplates add more stress to a transom....maybe but I doubt it. Why do I doubt it, because the higher you jack, the less drag you make, the less drag you have, the less that lower unit is trying to kick up and fight against the forward thrust of the prop. The less fighting the less stress and that is my theory and I am sticking to it. What is your theory that they contribute to transom stress? |
| lhg |
posted 02-10-2003 05:18 PM ET (US)
Sounds like ContinuousWave/Classsic Whaler has spawned yet another "Classic" boat brand site. I wonder if the Mako factory is participating? |
| logan |
posted 02-10-2003 05:54 PM ET (US)
I dont really know if a jack plate is bad or not, but the amount of drag on the lower unit makes very little diffrance regarding stress on the transom. the drag is mostly nulified by the thrust from the prop. more stress may be created from moving the force of thrust (prop) away from the transom (fulcrum) thus creating a larger lever. take a vice grip and attatch it to some mettle try to bend. then attach a lognger handle and it is much easyer to bend. or just push harder. same as puting a larger motor back there. my opinion. but it could be bunk |
| captbone |
posted 02-10-2003 06:02 PM ET (US)
I dont think that the extra stress is created when you are running. I believe is when you are running in seas and the boat is coming out of water or pound thru. Having the engine that much higher and away will increase the force of the engine slamming down. The guy with the mako only broke his transom when the engine slammed back down. I believe that if he had no jackplate the results would not be as bad. |
| NEVER SCARED |
posted 02-10-2003 06:23 PM ET (US)
I also think a jackplate adds stress to transoms. Its amazing that engineers feel that 2 1/8" thick plywood is enough to support up to 1200 lbs of weight. Just supporting that much weight is tough, now add all the bouncing while trailering! Pick up a 10 lb rock holding it straight down. Now try holding that same rock straight out 90 degrees from your torso. Thats what a jack plate does to your transom. On the other hand, a transom in good condition and made well should be able to handle this stress, and jackplates seem to have many benefits. I always wonder why transoms werent designed like rope. Made to handle 5xs the working load. Never scared |
| captbone |
posted 02-10-2003 09:18 PM ET (US)
I completely agree, jackplates have their time and place. On certain set ups I see reason. But in MOST aplications people think that it will do more than what it really will. You can only jack it so high, you can trim almost as high so the shallow water ability you gain is not as much a you would think, maybe 3 to 5 inches. My view is that any boat that ventures into any ROUGH water should think twice about one. My 2 cents! |
| jimh |
posted 02-10-2003 11:34 PM ET (US)
You can apply this same thinking to bow rails. From a mechanical analysis, bow railings are terrible. You expect a bow rail to contain a 250-pound adult being slammed into it. The leverage is enormous. There is now way a few screw fasteners and a small end plate can withstand the bending moment. I hearby vote that all bow rails be removed and the gunwales be raised to a higher level if the boat boat is ever used in rough water. Only be containing the passengers within the molded portion of the hull can they truly be safe in rough water. Hey, it's the same argument being made about moving an engine off the transom a few inches. Don't get me started about seats and consoles. How can you even think of just bolting these to the deck with a few fasteners? Look at the stresses they cause. Tear out those consoles and seats and save your self and your boat in rough seas. |
| captbone |
posted 02-11-2003 12:48 AM ET (US)
Wow jimh, you are so smart. I hope my post about jackplates does not take anytime away from you [editing] and censoring peoples ideas,thoughts and postions. |
| mtbadfish |
posted 02-11-2003 12:59 AM ET (US)
Oh-Oh |
| logan |
posted 02-11-2003 01:00 AM ET (US)
Well if not from changing the leverage, where does the added stress of a jack plate come from, and how much stress is added? ahh me spellchecker worked this time |
| jimh |
posted 02-11-2003 01:08 AM ET (US)
I don't recall editing or censoring anything you have said in this message thead. I just took the same concerns you have about the mechanical integrity of one boat component (the transom) and applied it to a different component (the bow railing). Discussion of issues like this is precisely what people come to the forum to read. Everyone must act as an advocate for their opinion. I just took the doctrine you are advancing and applied it to some other parts of the boat. If I have incorrectly applied your model of analysis to the bow rail, you should point out the error of my way. You are free to do this, without censorship. To decry that I am censoring you on this topic is, in my opinion, an attempt to deflect the issue away from the real discussion--mechanics of transom and engines--and on to an unrelated issue (alleged censoring of the forum content). If you wish to conduct a discussion about how I censor the forum, please post to the META-FORUM. But if you want to discuss the mechanical integrity of mounting heavy components on lever arms, this thread is the place at the moment. I also should point out that the mounting of most seats in the cockpit of most Whalers involves placing significant weight (as much as 500# for the case of two big guys on a leaning post seat) with a long lever arm (the seat pedestal). Should not we be concerned about this mechanical situation, too? |
| captbone |
posted 02-11-2003 01:17 AM ET (US)
If you have those people sitting on the rail in any kind of chop then the level idea comes into light for the bow rail. You have incorrectly applied this theory! If two fat guys are sitting on ped. seats while you are pounding thru ocean ways THEN it applies. But no one is ever going do this while in a chop or a sea. The way that you made your point was childish and it does not apply the same way and I hope you know it. You cannot just move the motor like you can a fat passenger to reduce the strain. |
| captbone |
posted 02-11-2003 01:18 AM ET (US)
How many people here sit on the bow rail while pounding thru any type of chop? |
| j_h_nimrod |
posted 02-11-2003 03:54 AM ET (US)
The whole point is the purpose and intended use/function of an object. Bow rails are not meant for continual strain whereas the transom is so intended. It is like saying theat we should do away with tires because they wear out. Maybe transoms should be removed and motors should become integral to the hull? It is a given that brackets put more stress on the transom, but this stress can be spread out over a larger or smaller area to take advantage of the entire transom thereby negating the extra stress. I dislike extentions/jackplates because at rest they lower the transom, a extention with flotation will not do this, but it will negate some of the positives of the extention. So six of one and a half dozen of another... So many options and opinions, can't we all just get along? rambling... |
| Bigshot |
posted 02-11-2003 11:42 AM ET (US)
Because some take a semester of Physics and think they have a theory....which is wrong. If jackplates added that kind of stress, trust me they would be excluded in the boats warranty. Who uses a leaning post in rough seas?....everyone who has one, that is the point of a leaning post. Who leans against railings....PLEASE! If you also think that jackplates have no "real" benefit, don't buy one but please do not bring your bubble gum science here and make a half assed argument. Give me some proof and then I will do some research on my end and consult some experts like Bob's jackplates, Boston Whaler, CMC, etc. I will take my whaler with my jackplate and you can take yours and we will see what benefits a plate has. I will also launch that boat higher in the air than you thought was physically impossible without a pilots license and let you make the call. |
| North Beach |
posted 02-11-2003 12:15 PM ET (US)
Aaah, back to normal. I am not sure exactly what a jackplate is--Is there a picture of one somehwere on this site? Is the sole purpose to move the engine level higher for better draft, maybe more speed? |
| hooter |
posted 02-11-2003 12:19 PM ET (US)
Seems the captain could have just as emphatically made an alternative, but consistent, pernt about why he hates hammers or garbage cans; hammers, because they hurt when you whack yer thumb with'em and garbage cans, because that's where mah wife throws mah favorite underwear right when they's gettin' comfortable. Mah pernt is that hammers and garbage cans and jackplates all have purposes that nothin' else can serve quite as well. Each o'these items can also be misused to regrettable effect in a variety o'ways. Gettin' all woiked up with exclamation pernts and all over jack-plates, though, get serious. Ain't nothin better f'gettin' into shoal water than a shallow draft boat wid a jackplate. A floatated transom bracket like the WhalerDrive (that's not a jackplate, by the way) does a marvelous job o'stretchin' the keel length of a hull t'better effect. Use a true jackplate on a boat t'run a ocean race from Lauderdale t'Bimini in a hurricane, and yer friggin' silly. |
| Bigshot |
posted 02-11-2003 01:03 PM ET (US)
Don't mind me kids...having an "off" morning. Hooter you are correct but I will say that many outboard offshore raceboats are using power jackplates to get a good holeshot(down) and top speed(up). You are right about the hurricane though. |
| WhalerGoFar |
posted 02-11-2003 01:24 PM ET (US)
I visited the Mako site and if the event you are referencing is the boat owned by Eddie Ring, then I think you should look a lot further then the Jack-Plate to lay blame. It would appear to me based on the pictures, discription of event, and weak condition of the transom should carry more of the blame then the Jack-Plate. I also noted that the owner didn't blame the Jack-Plate, seeing he put it right back on his boat. My 2 & 1/2 cents! |
| Vek |
posted 02-11-2003 02:51 PM ET (US)
Wayward thoughts from a distracted engineer... Jackplates. Two key effects during boat operation, one key effect during trailer transport. Operation: My numbers are quite crude, but operationally, indeed the two effects imposed by a jackplate cancel to some degree. Towing, the dead-weight torque described is present all the time, so that's the only problem I see. Address it by using a large backing washer or plate on the top bolts when mounting the jackplate to the transom to spread the load. -JV |
| DaveH |
posted 02-11-2003 02:59 PM ET (US)
My,my. The arm-chair engineers are out today. To answer a few: Yes, Jack Plates do cause more stress to a transom. This is not usually due to static engine weight but rather increased multiple moment stresses caused by dynamic forces. I would explain more but it would require more than a semester of basic Physics (thanks for the great nose tweak, Bigshot. I laughed). No, engineers don't "feel" 2-1/8" plywood is good for transom material. We design based upon known mechanical properties of materials and test samples when there is no data on experimental materials. Yes, most designs have built-in safety factors (higher factors in designs such as bridges, lower factors in aviation when weight affects performance). A single deck plate is part of a "system" of deck plates tied together by rigid tubing; think spider web and you'll appreciate the railing design more. This spreading of the load to a larger surface area can be related to the transom, lean posts, rope, etc. Like life, compromises must be made. Jack Plates are a compromise between increased performance and stress, added weight, seakeeping ability and cost. Most find the benefits are applicable to their boating needs. |
| Bigshot |
posted 02-11-2003 03:31 PM ET (US)
Whatever! When my transom falls of from both the jack plate and my "heavy" 4 stroke....you guys can all say "I told you so!" Until then, I have one of the sweetest, efficient, quietest, smokeless, non-fuel burning, less drafting, rig on the water. I have always been told HP ruins transoms, not weight, static trim, setbacks, etc. With all the hard groundings I have done in my boats over the years and on a daily basis when young, a jack plate or 50lb heavier engine won't do SQUAT to a Whaler transom. Nothing is more stressing to a transom than a WOT holeshot and a WOT sandbar encounter. |
| DaveH |
posted 02-11-2003 03:43 PM ET (US)
With all the hard groundings I have done in my boats over the years and on a daily basis when young, a jack plate or 50lb heavier engine won't do SQUAT to a Whaler transom Exactly! Boston Whalers and most other boats are designed for much more. Jack plates are fine. Captbone's opening statement is an opinion without basis. |
| captbone |
posted 02-11-2003 08:05 PM ET (US)
The basis is that they add stress. How much do you gain from a jacket plate? Why would you want to add stress? And with all of my bubble gum science and a semster of science, some people think that just because you lean against a leaning post it takes your full wieght like a jack plate???? A leaning post does not even take 1/3, some people have something call legs that take most of the wieght. Whatever????? |
| acassidy |
posted 02-11-2003 08:21 PM ET (US)
Has anyone here ever done test on their boat without the jack plate and then add a jack plate with the same motor and have results of the performance differences. It would be good to post performance tables of whaler own’s results with jackplates for MPG, top speed before and after. It is obvious jack plates add transom stress, but let face reality here. We are not talking about a 12” set back with a 600lb motor. (Very good reading on jackplates is in the Bass and Walleye magazine-which I have been a subscriber for 7 years.) Anyway I would like to add one to my Montauk but would like to know really the benefits of one. Archie |
| captbone |
posted 02-11-2003 08:31 PM ET (US)
Alot of mags like hotboats and B&W boats do test like this all the time, adding and removing jackplates and the benefit is a 3 to 4 mph but that is on a high performance boat with a v6. Unless you are going to put a lowwater pick up and jack it way up with a surfacing prop, which 99% of whaler owners would NOT, I do not beleive that you will gain so much. People hare like the look and way that they get to customize their boat but what is the real gain? |
| Wild Turkey |
posted 02-11-2003 09:21 PM ET (US)
captbone: Here is my gain: 1988 Montauk (not exactly a high performance boat) before: This performance is nice but I also enjoy the bow up attidude of the boat at cruise. |
| captbone |
posted 02-11-2003 09:42 PM ET (US)
A gain of 400rpm seems alittle high to me. If you would have moved the engine up a hole I think it would have been closer. If those numbers are right and you dont go offshore then I would say that a jackplate is worth it in your application. |
| andygere |
posted 02-11-2003 11:03 PM ET (US)
For the record, water intrusion is the leading killer of wood-cored transoms. While we're at it, let's get our terms right too. Stress is force per unit area. Strain is the deformation of an object caused by an applied force. These terms cannot be used interchangeably, however they are related. A useful article that explains this relationship, for those that really want to understand what is going on, can be found here: http://www.key-to-steel.com/Articles/Art43.htm By the way, a transom is not simply 2-1/8 inches of plywood; it is a composite structure consisting of wood, glass fibers and polyester resin, and it works as part of a larger structure, the rest of the hull. -A genuine, licensed, non-armchair engineer |
| TightPenny |
posted 02-11-2003 11:28 PM ET (US)
It is always nice to see others of the licensed persuasion around. |
| Bigshot |
posted 02-12-2003 08:52 AM ET (US)
My benefit is 5" less draft which is the difference between making it and getting stuck. I also can dial in the right height without unbolting the engine and using a hoist, not bad for $135. |
| DaveH |
posted 02-12-2003 07:42 PM ET (US)
I'd like to state for the record that my message directly after Vek's was a coincidence in timing. It appears after rereading in sequence that the comment of "armchair engineer" was directed at Vek. We have emailed each other to ensure that was not the intention but I feel it necessary to clear up the misunderstanding to the rest of you readers. The comment was directed at the nonsense prior to Vek's message. Regards, |
| captbone |
posted 02-12-2003 08:47 PM ET (US)
Since we have so many smart people here, I would like someone to do their magic formula and tell me the force of an motor reentering the water after a wave like that shown on page 40 of pics. I would certainly not want a jackplate of that boat in that situation. The extra force on that transom must be HUGE. |
| jimh |
posted 02-12-2003 11:36 PM ET (US)
With respect to "smart people" on the forum, I hope that is not being used sarcastically. There is the ocassional 14-year-old asserting himself as an expert, but in the main I think that the majority of people who contribute in the forum are well versed and well schooled in the subject areas they participate. There are quite a few holders of doctorates, professors, and other professionals who regularly post articles here. I include licensed Master Mariners in that group, too. |
| captbone |
posted 02-13-2003 12:01 AM ET (US)
thank you, i did not mean that sarcasticly, I am in pursuit of my MBA at the persent time but like most people who are not engineers I could either look up the formula or ask someone. I am asking. I never meant for this post to get pissy, I in the past I have been against jackplates while others swear by them. People have said that I can not back up my reasoning, I have tried. As a participant in this great site I would like to shine light on the fact that jack plates do have faults. Even though few if any back me up on this. Since I am not an engineer I can not give the math but one of my key points is on page 40 of pics. The forces on that transom are truely great. I beleive that a jackplate will increases those forces almost expencially. |
| Bigshot |
posted 02-13-2003 10:18 AM ET (US)
Capt....That pic of Tom is a great one but....if you look carefully the bow is really high, not the stern. I have had my engine(no BS) 6-8' off the water on too many occasions to mention. That means my bow would be 15+' off the water. If you do not believe me I have a list of phone numbers you can make to back up that I am the Evil Kinevil(sp?) of barnegat inlet. I have had the coast guard just shake their heads at me like i was nuts....and I am. I have never had a stress crack on any of my Whalers. That is why I own them. I had a Glastron and the 1st time out the inlet the floor cracked and the windshield fell off and I never got the prop out. My bud tried following me in his 18' SeaRay and the seat broke and the floor cracked as well. If I had a Carolina Skiff....I might not choose a Jackplate, on a Whaler, you can't hurt that transom, jackplate or not. |
| captbone |
posted 02-13-2003 01:46 PM ET (US)
Point well taken, I guess I related a whaler to much to other boats. I always love seening those pictures. |
| Seabrook |
posted 02-13-2003 05:31 PM ET (US)
I am always amazed at how complicated some of these threads get. It does not take an engineer to know that anytime you move the motor further away from the transom, it will create additional stress. I can't see how the height would make a big difference, but the distance from the transom will give the motor more leverage and therefore more stress. No one can argue that. But...I think the transom on a quality boat can handle the stress with no problem. That being said, I have a jackplate on my boat and could not imagine not having one. That is the first thing I added to my 18 Outrage when I bought the boat. For me it is not about performance, but rather to get across shallow areas when the tides are low. And yes...just a couple of inches can make a huge difference with a hard sand bottom. While you can trim your motor and gain some height, you also will push your bow up and your transom down unless you are running at high speeds. A jackplate allows me to run on a minimum plane and raise the motor. When I am worried about hitting bottom, I prefer not to run at high speeds. I have the jackplate mounted as high as possible on the transom and the motor mounted as high as possible (bottom holes) on the jack plate. Yes it will cavitate a little, but will run real shallow. Just watch the RPMs and the water indicator. Then when you go offshore in rough water, just lower it back down to normal. Yes, I love my jackplate. |
| 11 footer |
posted 02-13-2003 06:34 PM ET (US)
jimh, In your last post you said something about a 14-year-old asserting himself as an expert. I'd like to now if the person is me. Not a need for a long reply, just a yes ot no. 11 |
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