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  1. #91
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    Out of curiosity why did you stop the transom short of the bottom of the boat...is that the way the old transom was?
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  2. #92
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    Ok, the transom is four layers of foam?? What keeps the screws from compressing the foam????

  3. #93
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    Quote Originally Posted by DanUmbarger View Post
    Out of curiosity why did you stop the transom short of the bottom of the boat...is that the way the old transom was?
    Nothing is applied that low other than the motor push (if you will) the built up thickness is just under 1/2" (plenty strong)

    Wood transoms are usually installed @ the bottom, sealed poorly, and any water in the boat sits @ the bottom looking for away into the wood.
    I've seen them as I built mine, built a few wood restores, and just felt better about the wood being above all the trouble, also no drain plug thru wood.

    Seemed like a good idea @ the time.
    Wriggleys gum makes me think of boating, "Double your engines, Double your fun"



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  5. #94
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    Quote Originally Posted by 1954bmw View Post
    Ok, the transom is four layers of foam?? What keeps the screws from compressing the foam????
    I'm gonna take a crack @ this, maybe somebody with a working brain will step in and save me .... or not

    the foam is rated at 80 lbs. per square inch, 2" washers times 3.1416 = 6.2832 square inches of surface x 80 lbs. = 502 lbs. to crush the transom.

    I have a support plan to carry the weight of the motor/bolts so it doesn't saw its way down thru the transom. The bolts only have to be tight enough to keep it from moving around.

    Wish me luck.
    Wriggleys gum makes me think of boating, "Double your engines, Double your fun"



  6. #95
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    wish you lots of luck, keeping an eye on this

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  8. #96
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    Now that you have experienced the FOAM in the transom... you can use a 6# foam to fill those floor stringers by dipping the bow and raising the transom. This will allow you to pour into the cut areas, completely filling the voids, adding tons of structural integrity and giving your fasteners something to grip to. If you think it out... you can pop in nut-serts and the foam will lock them in place if you decide to build a floor you could remove later in life or cut in access panels.

    I used the foam from USComposites and they have been very helpful in choosing the right materials. Many of the local boat manufacturers here in the Carolinas use their products in their OEM builds for structural impact resistance on offshore boats. I used the 6# in my Eliminator Daytona rebuild.

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  10. #97
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    Just add a little x-tra glass to the area the bolts go thru. No big deal, you wont compress the foam with the normal motor bolt tq. of 40 lbs. The foam is tougher than you would think.

    83 V-King, 96 Mariner, 200 hp ff block 2.5 w/a 28p choppa
    We gotta clean this liberal mess up, VOTE TRUMP TO MAGA!
    Rebuild thread:
    http://www.screamandfly.com/showthre...-it&highlight=
    http://www.screamandfly.com/showthre...cs.&highlight=
    Videos

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  12. #98
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    I think I've got the crush problem solved. I cut the back out of the splash well and ground it to fit the transom.

    I am going to use the back and top of the transom to cast a new splash well back. It will be 5 or 6 layers of 1700 (over the top and down the inside) cast with mold release. when cured , pop it loose, bond to splash well, finish.

    Now I have a 1/4" thick x 30" wide "washer" to protect the transom and carry the motor weight.

    Click image for larger version. 

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    Wriggleys gum makes me think of boating, "Double your engines, Double your fun"



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  14. #99
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    Guys, first let me say that I do not know anything about using foam as a stressed member. I have used 2lb foam under the gunnels, in flotation boxes, and 4lb foam in the floors. But the assumption that the load on the bolts is only 40 lbs is not quite the whole story. I did an article for Bass&Walleye Boats magazine years ago wherein my research showed that a 125 horse outboard could generate as much as 1130 lbs of thrust at the propshaft (depending on pitch and diameter) and those 1130 lbs would generate 2,420 lbs/ft of force 20" away at the top of the transom even with zero (0) setback. The article was written to show how important the proper use of the correct fasteners and transom maintenance is. I conducted several interviews with different boat manufacturing heads and got their takes on bolt materials, sizing, and clamp loads. One company used 6 1/2" bolts (4 top, 2 bottom) and I remember specifically that Darris Allison was and had been using 9/16" x 18p top bolts years earlier. The 40 lbs of tightening torque is only part of the stress our transoms must live up to. Gordon

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  16. #100
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    I'll mention too that the towing/trailering forces are nowhere near the forces generated in the water at full thrust. I calculated that a 400 lb outboard with 0" setback hitting a pothole generating a 2" deflection at 30 mph would generate a force of 492 lbs (1/44th of a second). Gravity causes an object to fall 32 feet per second per second. Speed that same pothole hit to 60 mph and the force goes to 580 lbs (1/88th of a second). Add setback and horsepower and these numbers go up quickly, but that is not the topic of this thread. Gordon

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  18. #101
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    But yet the foam transoms work out quite well......I have seen no failures when they are glassed properly. When I started using foam transoms back in the early 80's I sleeved them with s.s. tube to avoid compression, found out after a while it was not needed.

    83 V-King, 96 Mariner, 200 hp ff block 2.5 w/a 28p choppa
    We gotta clean this liberal mess up, VOTE TRUMP TO MAGA!
    Rebuild thread:
    http://www.screamandfly.com/showthre...-it&highlight=
    http://www.screamandfly.com/showthre...cs.&highlight=
    Videos

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  20. #102
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    My concerns are with the math. Above, NP mentions 80 psi and a calculated 502 lbs compression capacity, but the 40 lbs/ft you refer to is strictly the measure of rotational force applied to the bolt/nut tightening torque. That is a lot different that "clamp load". A Grade 5 1/2" x 13p bolt has a clamp load of 9,000 lbs. A 1/2" x 20p has a clamp load of 10,250 lbs. Either the 502 lbs capacity is all wrong or the 9,000 lbs clamp load will crush it.

    Give this some thought - a manual jackplate having a single threaded lift bolt in the center of the jackplate easily lifts the 500 lbs of motor with just a couple lbs of force. A scissors jack easily lifts a 4,000 lb car with the simple turn of a 1/2" threaded bolt with something a lot less than 40 lbs of twisting torque. I'm a skeptic, I'll hush now and learn........Gordon

  21. #103
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    Found a chart - This one is Grade 5 since Stainless Steel fasteners are not available exceeding this rating.

    Attachment 424301

  22. #104
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    Agree with some up here - rotational torque of 40 ft/lbs is indirectly proportional to the clamp force. I'm no math wiz, but tightening the bolt to 40 ft/lbs is going to be a lot more than 40 lbs of pressure clamping the transom.
    You're talking hundreds and hundreds of clamp pressure. Borderline of your foam psi. Granted, I'm sure a bit of fiberglass where the washers hit will help out a ton.

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  24. #105
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    Quote Originally Posted by 1954bmw View Post
    Ok, the transom is four layers of foam?? What keeps the screws from compressing the foam????
    Quote Originally Posted by NICE PAIR View Post
    I'm gonna take a crack @ this, maybe somebody with a working brain will step in and save me .... or not

    the foam is rated at 80 lbs. per square inch, 2" washers times 3.1416 = 6.2832 square inches of surface x 80 lbs. = 502 lbs. to crush the transom.

    I have a support plan to carry the weight of the motor/bolts so it doesn't saw its way down thru the transom. The bolts only have to be tight enough to keep it from moving around.

    Wish me luck.
    Quote Originally Posted by Gordon02 View Post
    My concerns are with the math. Above, NP mentions 80 psi and a calculated 502 lbs compression capacity, but the 40 lbs/ft you refer to is strictly the measure of rotational force applied to the bolt/nut tightening torque. That is a lot different that "clamp load". A Grade 5 1/2" x 13p bolt has a clamp load of 9,000 lbs. A 1/2" x 20p has a clamp load of 10,250 lbs. Either the 502 lbs capacity is all wrong or the 9,000 lbs clamp load will crush it.

    Give this some thought - a manual jackplate having a single threaded lift bolt in the center of the jackplate easily lifts the 500 lbs of motor with just a couple lbs of force. A scissors jack easily lifts a 4,000 lb car with the simple turn of a 1/2" threaded bolt with something a lot less than 40 lbs of twisting torque. I'm a skeptic, I'll hush now and learn........Gordon
    Hi Gordon, did you read my post on the crushing of the foam? A Canadian friend of mine was worried about the same thing, and as I told him .... I dunno seems like it should work. ;-)

    I then went to my shop and did some bonehead test with a piece of 1/2" 80 lb foam, a 1/2"-13 tread bolt, 2) 1 3/4 dia washers and a 1/2" nut, and a torque wrench.

    Bare foam supported 50 foot lbs bolt torque with barely any marks on the torque side and no marks on the back side.

    Click image for larger version. 

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ID:	424303 At 65 foot lbs it showed considerable compression on torque side and some on the back.

    1/2" foam with only one layer of 1700 cloth and epoxy resin on both sides showed quite a bit better.

    100 ft pounds torque showed a light compression and 125 ft pounds didn't do much more. back side @ 100 showed -0- depression
    backside @ 125 showed light compression.

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    The outer glass (original transom skin) is 1/8-3/16 thick, next 1 layer matt & 1 layer 1700, 1layer 1/2" 80 lb foam.
    next layer : 1700 + layer of 1/2" 80 lb foam
    next layer : 1700 + layer of 1/2" 80 lb foam
    next layer : 1700 + layer of 1/2" 80 lb foam

    There are 3 layers of 1700 + epoxy as finis on inside, there are 2) more layers of 1700 between the inner knees ( witch reduce the transom span from 5' to 3'

    The new splash well back wall will cap the transom (vertical load) add to the front of the transom 1/4" of 1700+ resin.
    I would guesstimate 3/8" + glass thickness @ top bolts.

    Motor plates will spread the load on the outside, slpash well on the inside.
    I think 1/2" bolts, washers, nylocks -------- 25-35 foot lbs torque will be more than enough.

    I'm thinkin I'm OK ............... I have been wrong before, probably not this time.

    Thanks for your concern, please keep watching. NP
    Wriggleys gum makes me think of boating, "Double your engines, Double your fun"



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