Outboard brackets and motorization

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Christer
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Outboard brackets and motorization

Post by Christer » Sun Dec 23, 2018 5:38 pm

Still planning my planning to build a boat...

Two questions popped up in my head all of a sudden. The first has to do with outboard brackets and transoms, the second with motorization.

Brackets and transoms first. If building a boat that has a full transom option as well as a regular motorwell transom with the required angle for mounting the outboard, the full transom version will necessarily have the same angle. Is it feasible/possible/advisable to change that transom angle for stylistic reasons, or would there be structural considerations? I'm partial to a more forward slanted transom depending on the boat and style of the boat overall, and with a full transom there would be a custom made bracket for it in any case. Would a "reversed" transom impact the mounting of the bracket in any way, particularly with regards to how forces are transferred through the structure?

Secondly, for a large-ish planing boat, is a twin outboard setup a better way to go than a single? Apart from the doubling of everything and a little more weight. Say 2x125HP vs 1x250HP; would the twin setup deliver better fuel economy than a single? Would the twins work harder than the single or would there be less stress and wear since there are two outboard to handle the workload? The obvious advantage is that if one outboard develops a problem at sea, there's still a second to get you home somewhat fast, whereas with a single you're stuck.


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silentneko
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Re: Outboard brackets and motorization

Post by silentneko » Mon Dec 24, 2018 6:47 am

Pitching the transom to the bow is not a huge deal structurally I would think, but you gotta realize you are sacrificing a lot of interior space doing it. On my FS17 if I just reversed the angle (14 degrees I think), I would lose about 7" of interior space. On a larger boat like you are talking about it can be a foot or so. That's a big deal especially if it's a fishing boat, just to add a touch of styling.

On twin outboards vs single, it comes down to weight and drag. A single outboard will run faster and use much less fuel then twins equaling the same power. Twin setups will add weight to the transom, additional rigging, and you are dragging another lower unit through the water. With today's reliability on newer motors most guys I know have ditched twins. Instead they make sure to have a good seatow package, a good anchor, and safety equipment like epirbs and plbs.
Built: 15ft Skiff, 16ft Skiff, Modified Cheap Canoe.....FS17 coming soon!

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BarraMan
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Re: Outboard brackets and motorization

Post by BarraMan » Mon Dec 24, 2018 7:17 am

One of your twins will most likely NOT put the boat on the plane, so you will be coming home at displacement speed only. That being the case you are better off with a big single and a high thrust kicker (auxillary).

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OrangeQuest
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Re: Outboard brackets and motorization

Post by OrangeQuest » Mon Dec 24, 2018 8:04 am

When it comes to multi-engines verses single you have to consider what the purpose of the vessel will be. Fishing/family boat that needs to be cost effective on both purchase price, fuel costs and maintance costs. More props in the water will give you better hole shots or if you are planning on using the boat to tow heavy things like a rescue vessel or something like that then more props in the water will be better than a single. One big motor will be cheaper to buy, cheaper to keep fuel in it at different cruising speeds and cheaper on maintance costs.
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Re: Outboard brackets and motorization

Post by fallguy1000 » Mon Dec 24, 2018 9:59 am

Generally only in boards have reverse rake transoms
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Re: Outboard brackets and motorization

Post by jacquesmm » Mon Dec 24, 2018 2:39 pm

About transom angle and brackets.
Outboards have a clamp to fit a transom angled 13 degrees, give or take one degree. You can't change that.
Brackets are angled the same 13 degrees on the outboard side and 13 degrees on the boat side. That's because all transoms are designed to take an outboard at 13 degrees.
If you want to mount a bracket on a vertical or reverse transom, you will have to order a custom made bracket.

No problem with the structure if the boat is designed to take an outboard but if you are thinking of mounting a bracket on an old boat designed for inboard, you have a problem. An inboard engine transmits its force through the shaft to the engine beds while an outboard pushes the boat through the transom and stringers, a very different concept.
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Re: Outboard brackets and motorization

Post by Fuzz » Mon Dec 24, 2018 2:45 pm

I am in the single with a good kicker camp but that could be because that is what I have. I saw an Utube test done by Yamaha using two identical boats, one with a 300 hp single and one with two 150's. The end result was they were so close that it did not matter. Each boat won and lost different things but in the end it was a flip a coin deal.
Not too long ago I was on a 27 foot boat with twin 200s. It was propped to run mid to upper 40s. One engine went down and 6-8 knots was all we could do. A good kicker could have done just as well while using much less fuel. BUT the extra power could have come in real handy if we had been fighting high winds and waves.
So I say go the way that makes you happy, that is what really matters :wink:

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Re: Outboard brackets and motorization

Post by fallguy1000 » Thu Dec 27, 2018 9:50 am

jacquesmm wrote:
Mon Dec 24, 2018 2:39 pm
About transom angle and brackets.
Outboards have a clamp to fit a transom angled 13 degrees, give or take one degree. You can't change that.
Brackets are angled the same 13 degrees on the outboard side and 13 degrees on the boat side. That's because all transoms are designed to take an outboard at 13 degrees.
If you want to mount a bracket on a vertical or reverse transom, you will have to order a custom made bracket.

No problem with the structure if the boat is designed to take an outboard but if you are thinking of mounting a bracket on an old boat designed for inboard, you have a problem. An inboard engine transmits its force through the shaft to the engine beds while an outboard pushes the boat through the transom and stringers, a very different concept.
An excellent point I failed to make.
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Re: Outboard brackets and motorization

Post by OneWayTraffic » Sat Dec 29, 2018 2:11 pm

If going twins I would go with Etecs for the greater grunt low down should you be ever caught with one engine.

How likely is that though? Plenty of things that put down one engine will do both (fuel, prop strike).

Single plus kicker may be more effective.

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Re: Outboard brackets and motorization

Post by cracked_ribs » Sat Dec 29, 2018 6:03 pm

OneWayTraffic wrote:
Sat Dec 29, 2018 2:11 pm
If going twins I would go with Etecs for the greater grunt low down should you be ever caught with one engine.

How likely is that though? Plenty of things that put down one engine will do both (fuel, prop strike).

Single plus kicker may be more effective.
Etecs on one of the designs here would be one of the few applications in which I'd say you could probably stay on plane pretty well with only one of your twins working. They're so torquey and the designs here are so light and efficient that if you were anywhere near the upper end of recommended power - say a CS25 with a pair of 150s - I'll bet a single G2 150 even propped for twins would launch one of those onto plane no problem. The 150 HO would probably plane it in fairly rough weather.

But my experience is also mostly single with kicker. If money was no object I would take twins but so far in my life money has been a consideration and a single with a kicker has been adequate. Ownership is cheaper, maintenance is cheaper, fuel is cheaper, reliability is comparable.

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