My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

[runninfarmer]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

Have you considered something like this? You mentioned that you would like something adjustable. The white and green pieces have holes drilled in them, and you could raise or lower the drive by adjusting the bolt holes on those two pieces. Use two bolts in the middle spaced apart attaching the white and green pieces so they don't collapse. This orientation would also make it overall more rigid. Just a suggestion.

View attachment 194617

Prolly a good idea to put diagonal members in. I have extra angle to do it, just have to take a breather on it for a while, lol. Been going hard at it for a couple weeks. I don't think it's physically possible for it to collapse with the way I have it, unless there is a failure at the middle members. But the suggestion is noted.

 

[chriscraft254]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

I was thinking the opposite, since the center of gravity shift will coincide with where the majority of your passengers are. I think it should help with having extra weight in the back of the boat, since the "lever arm" is lengthened. If you think of the outboard as a pivot point, if it sits farther back, identical weight in the same position should keep the bow from rising as much. You have a 19' lever vs a 21' lever, with weight being put on identical positions, with the pivot weight being shifted back 2'. Here's a pic to describe what I'm talking about:

View attachment 193476

The drawing isn't to scale, but it gives you an idea of what I mean. Also, putting on an offshore bracket is supposed to increase propeller efficiency, since it runs in less turbulent water and for a couple reasons. This is better explained in this link which is all about offshore brackets:
Classic Whaler: Boston Whaler: Reference: Engine Brackets

I think your thinking is wrong here. Your not taking into consideration that the displacement/floatation spread of the hull helps when the motor is on the transom of the boat. If the boat was an I/O before that puts more weight in the boat than you had hanging over the back, so even more of a balance issue. With the motor moved back 2 ft plus, it will make your boat not ride right without adding floatation pods. On a heavier boat and more length I think this may work fine, but on a boat of this size I think your asking for problems. Love to see a pic of the boat sitting in the water without people aboard to see how far down in the water the motor is sitting. Hope I'm wrong, good luck and be careful.

 

[runninfarmer]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

Yeah, I'd be lying if I said I wasn't nervous about it. It will be interesting. I'll prolly do a float test this week. If it sits too low, I'll just rig up some type of bouy to throw in the framing of the bracket. Nothing ventured, nothing gained.

 

[m casey stock]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

Brackets are nice because they preserve the top half of the transom. I was thinking it'd be wrong to cut into it and butcher it.

That being the case, you could always shorten the outset to a minimum operating distance if it doesn't workout with it like it is and all the hard work would at least not go to waste. I don't know, 2ft may already be the minimum. Or trade for a long shaft motor. Didn't you say this one is a short shaft?

 

[jasoutside]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

Yeah, I'd be lying if I said I wasn't nervous about it. It will be interesting.

I'm nervous too.:nonchalance:

I can see that whole set up folding up on itself and torquing right over :cower:

 

[GA_Boater]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

Hey runnin' - Great ingenuity and thinking outside the box. I do have one concern. The strength and reliability in structure comes from triangulation. The side verts aren't angled enough, are almost parallel to the ends and could become the single point of failure. If either bolt lets go or loosens, the bracket will fold up. nickypoo has the right idea to add an angled strut. Think about it.

Also when you have proven the concept, do consider welding the bracket. You will be getting tired of checking bolt tightness before and after every launch. The one time you forget ..... well lets be positive, weld it before you call it done. Good luck.

 

[bob johnson]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

well, if it were simple they wouldn't be making $2000 brackets. One key is the size of the motor. Most brackets are over built , so if later on a motor is changed out to a heavier one, they don't end up with egg on their face. I would'nt attempt what you are doing with out TWO bolts per side per end... second I don't see why you made the set back to LONG??? I am making a bracket, and I could have bought and or made the simple motor mounts, but that cantilevered motor will pull the stern down!! so I am building mine with full floatation pod underneath!!! ONE of the absolute biggest issues you will have with your design is trailering your boat on poor roads...it will try to rip your boat and transom apart.... the stresses of the bracket under use in the water is NOTHING compared to what it will encounter on the road...the boat is fixed on the trailer and the motor is dynamic!! in the water the boat and motor are BOTH dynamic....good luckbob

 

[Last Mohican]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

Glad to hear you are considering a diagonal member. Looks like you are making some progress. Sometimes it is a joy in making it yourself that makes it worth it.

 

[runninfarmer]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

Yeah, the float test will tell a lot. I chose the long setback because I based it on the length of the "pods", though I wasn't thinking of their displacement aspect. I was also thinking at the time that I'd need tilt room for a straight 6 Merc if I threw that on. If it's able to float ok at current setback, I'll just have my neighbor weld all connections for rigidity. Other wise I may have to pull the motor and shorten the setback. Theories are theories until experimentally proven or disproven, that's what I do for a living. I don't disagree it may porpoise and the bracket will need some more rigidity, but if it's never been done before we can't know for sure what will happen at the dock. I'll be putting it in slow for sure at the ramp.

 

[saginawbayboater]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

well, if it were simple they wouldn't be making $2000 brackets. One key is the size of the motor. Most brackets are over built , so if later on a motor is changed out to a heavier one, they don't end up with egg on their face. I would'nt attempt what you are doing with out TWO bolts per side per end... second I don't see why you made the set back to LONG??? I am making a bracket, and I could have bought and or made the simple motor mounts, but that cantilevered motor will pull the stern down!! so I am building mine with full floatation pod underneath!!! ONE of the absolute biggest issues you will have with your design is trailering your boat on poor roads...it will try to rip your boat and transom apart.... the stresses of the bracket under use in the water is NOTHING compared to what it will encounter on the road...the boat is fixed on the trailer and the motor is dynamic!! in the water the boat and motor are BOTH dynamic....good luckbob

Agreed!! Pounding it down the road is hard on it. Hopefully you won't be driving and look in your mirror and see your motor and bracket being drug by the steering cable

 

[GT1000000]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

Good point about the roads, especially pulling into and out of some driveways, where the angle of attack between the road and the driveway may cause some very serious issues...

 

[briangcc]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

I'd also add some bracing across the top and bottom from one side to the other. Right now, there's very little to keep those two horizontal arms from being bent parallel to the transom under a hard left/right turn.

And I'd seriously consider shortening that bracket or cutting the transom to allow an outboard. But that's just me...I over build and err on the side of caution.

 

[Nickypoo]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

Runninfarmer: If you take some measurements for me I can calculate the forces on the various bolts and transom to either give you piece of mind or give you an idea of what you need to change if some of the forces are too large.

 

[runninfarmer]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

I can get you some measurements some time. I haven't done much with the boat past couple days. I do have access to a 3D printer so I was able to to print out a 1/24 scale model of my blue fin by LXWXH. It's not exact but it will get the job done for some modeling. I used relative weighting to demonstrate possible porpoising people have been bringing it up. Based on what I can get from Nada, I assumed my hull is 1,000 lbs. With a 300 lb outboard, I let the outboard wt be approximately 30% of the boat weight. Using this fraction and knowing my scaled down boat weighs 90 grams, I did some tests with 35g of weight for the respresentative outboard, and 50g of weight for the representative OMC inboard setup that was previously used. I know 35g isn't 30% of 90, but used a little extra to count as the bracket. Here are pictures of the results, as well as a pic of an identical boat to mine that had the inboard setup:

This represents my boat with my current outboard setup and 30" setback


This represents the Inboard setup:


This is an acutal Blue Fin in the water


The tests demonstrated there was slightly higher bow raise with the current setback I have. I believe I will compensate for this though by placing 110 lbs worth of batteries and a 70 lb trolling motor on the bow. This doesn't include the bow seating which will be plywood, which will also help. The actual Blue Fin with inboard has a certain degree of bow rise. I've heard of displacement pods eliminating this (over buoyant), which I don't think is necessarily a good thing based on some reading I've done. I feel if I can mimic the previous bow lift as close as possible, should work ok. I also don't want to lift the motor again. I still like having the long setback due to potential performance benefits. I will beef up the bracket with more bolts and supports and possible welds after I have finished the flooring. I don't think I will have a porpoise issue, but won't know until the full completed boat is in the water.

 

[SigSaurP229]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

its a neat concept as it seems old tinny's are easier to come by in I/o, and I agree I would much rather have an outboard.

I think the biggest flaw in the design is that your bracket nearest the original transom needs two bolts rather than one. Eventually time and torque will loosen them and while the unit is structurally sound I think the whole thing will begin to sag. I don't think that there is any doubt that the aluminum will hold the weight I think the question is will the weight remain still and how will it affect the handling and center of gravity on the boat.

 

[Nickypoo]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

Cool work with the 3D printer.

 

[runninfarmer]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

Spent the last month rebuilding the floor and did some mods to the bracket. Shortened the setback by 14" and put in diagonal cross members to make it stronger. Should help move the COG up a bit. I also have 50lb battery and 60lb trolling motor on the bow. Should sit ok in the water. It's almost water ready. Here are some pics:

 

[blazin_jason]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

Looks better now!

 

[runninfarmer]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

I figured it was time to show a water pic. Had the boat out on the Grand River:


Here's a video of it at cruising speed:

Overall I'm pretty satisfied with how it performed. Helped having a smaller 4-blade prop and hydrofoil.

 

[jbcurt00]

Re: My Custom Offshore Bracket: I/O Conversion for less than $500, No Welder Required

Why is there so much water spraying the motor cowl?