mid range twins...

tod osier

tod osier

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I want to power my Tolman with mid range twins, something like 50's or 60's. Does anyone here have experiance with NON - counter rotating twin engines in that size? I haven't exhaustively searched, but it doesn't look like a mid range counter rotating engine is available in a configuration I want.

T
 
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it doesn't look like a mid range counter rotating engine is available in a configuration I want.
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Is that because you don't get the performance advantages at the lower hp/speeds? Just wondering because I see a lot of guys putting mid-range twins on their houseboats around here. Some are new boats; others are old inboard powered boats that they are converting into twin outboards. I've driven one of them and talked to a few others, and they've all been non-counter rotating--mostly mercs and e-tecs. Of course, we're talking heavy displacement hulls, so that may make a difference when looking at performance.

Rick
 
it doesn't look like a mid range counter rotating engine is available in a configuration I want.
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Is that because you don't get the performance advantages at the lower hp/speeds? Just wondering because I see a lot of guys putting mid-range twins on their houseboats around here. Some are new boats; others are old inboard powered boats that they are converting into twin outboards. I've driven one of them and talked to a few others, and they've all been non-counter rotating--mostly mercs and e-tecs. Of course, we're talking heavy displacement hulls, so that may make a difference when looking at performance.

Rick
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I'm interested in redundancy with decent performance. I'm sure it isn't done because it is not cost effective.

T
 
todd, the other thing to keep in mind is the extra weight of twins vs a bigger primary and a kicker. If I remember right that is Renns biggest complaint against twins. So you really lose out on the performance end because of the weight, they cost more, maintenance costs are higher. Personally, if I have a good kicker to get me home I'm satisfied.
 
Pete,

This would be on a Jumbo, and a pair of 4 strokes that size are under the 500# limit. I know the negatives of twins, I also know the positives. I don't want to say money is no object, but at this point I'm not concerned with the extra costs. I've owned an F40 for a long time, so I know the maintaince costs.

At this point a kicker doesn't do it for me, sure it is fine as a backup on nice days on protected water, but that isn't what I'm building the boat for. I have no need for a kicker for trolling for my style of fishing either. I may end up that way, but not starting out.

T
 
Todd,

I have run a few boats set up with small twin outboards (Cape Cruiser/C-Dory) powered with non-counter rotation twin 50hp or 60hp Yamaha's. You do not notice any adverse effects of have two motors rotating in the same direction. I would certainly reccoment using hydraulic steering to eliminate any possibilities of torque felt through the helm, but even at that there is not much to be lost by not using a counter rotating combo. You are correct, typically 115hp is the smallest hp that is offered in a counter rotation setup. I have thought quite a bit about building a Tollman skiff, or having Devlin design a smaller 22-24' skiff that could be powered by small outboards, and would without any hesitation use twin non-counter rotating 60hp outboards.
 
Todd,

I have run a few boats set up with small twin outboards (Cape Cruiser/C-Dory) powered with non-counter rotation twin 50hp or 60hp Yamaha's. You do not notice any adverse effects of have two motors rotating in the same direction. I would certainly reccoment using hydraulic steering to eliminate any possibilities of torque felt through the helm, but even at that there is not much to be lost by not using a counter rotating combo. You are correct, typically 115hp is the smallest hp that is offered in a counter rotation setup. I have thought quite a bit about building a Tollman skiff, or having Devlin design a smaller 22-24' skiff that could be powered by small outboards, and would without any hesitation use twin non-counter rotating 60hp outboards.
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Thanks Sean, that is the sort of hands-on advice I was looking for. I was thinking that no feedback steering would be an asset. I haven't started serious planning, but I want to be able to JUMP if I run across a great deal.

I am going to re-do my snowgoose this spring and start the tolman as soon as I get that done.
 
Also, if you compare the weight for this application of a single with kicker vs. small twins, the twins are actually lighter. For example, Yamaha 115hp 4 stroke (420lbs) and Yamaha T8 4 stroke kicker (110lbs) total of 530lbs vs. two Yamaha 60hp 4 strokes (238lbs) for a total of 476lbs. Also if you look at the cost differnce, twin Yamaha 60's with controls typically run about $7,000 per unit, vs. Yamaha 115hp ($10,500) and Yamaha T8 ($2,500), you are pretty close in the actual costs. True you do sacrifice some performance of using twins by having two lower units dragging through the water, but benefits certainly outweigh the disadvantages in most cases.

Sean
 
Also, if you compare the weight for this application of a single with kicker vs. small twins, the twins are actually lighter. For example, Yamaha 115hp 4 stroke (420lbs) and Yamaha T8 4 stroke kicker (110lbs) total of 530lbs vs. two Yamaha 60hp 4 strokes (238lbs) for a total of 476lbs. Also if you look at the cost differnce, twin Yamaha 60's with controls typically run about $7,000 per unit, vs. Yamaha 115hp ($10,500) and Yamaha T8 ($2,500), you are pretty close in the actual costs. True you do sacrifice some performance of using twins by having two lower units dragging through the water, but benefits certainly outweigh the disadvantages in most cases.

Sean
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Thanks for the added convincing.
 
pull starts of course....RIGHT?

Wouldn't want to have to worry about battery failure causing a problem.....

So when do you start building?

AND...we still on fo S.D. this Fall?

Steve
 
pull starts of course....RIGHT?

Wouldn't want to have to worry about battery failure causing a problem.....

So when do you start building?

AND...we still on fo S.D. this Fall?

Steve
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You can't get a 60 pull start, so no.

As for SD, we are on, unless I can find someone who is less of a jackass. :).
 
Tod,
I dont have one with the small 60's but we have a 115 pair on a customers boat at work.
They work and I think you will be OK.

The first time you run the boat in a full circle with one in fwd gear and one in reverse you will be happy. The twin handling can be a huge advantage in tight spots.

Lastly, a close friend makes the buying choices for a very well known towing and salvage company. Their small boats used to be jack shaft stern drive inboard diesel singles. They are now running twin 4 stroke honda gas. Very comforting to have a second power head to rely on far off shore. More options for moving a boat on the hiptow. Very good on fuel and maint.. I still love a single diesel work boat, but there are very good reasons commercial operators are using twins in the towing and salvage side.
True redundancy will require some extras like tanks and batteries.
Check out Balmar and Blue Seas for some good gear to set up the electrical system. Esp battery switching and charging.
 
Thanks Bob, I was hoping for a comment from you, thanks for the insight. I was for sure planning redundant fuel and electrical (as much as reasonable, anyway). I enjoyed my last build a lot and learning stuff like proper marine wiring. This build will for sure have some challenges.

T
 
Whats the advantage to counter rotating engines, as opposed to having them in the same
rotation? Torque cancellation? Vibrations smoothed out?

Just wondering.
 
Whats the advantage to counter rotating engines, as opposed to having them in the same
rotation? Torque cancellation? Vibrations smoothed out?

Just wondering.
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Geoff, yes, torque cancellation is the goal.
 
Tod, I am sure you have been on the Tolman site, but someone over there asked the same question fairly recently (within a page or two of the beginning).

One point that has not been brought up here is the fact that a 60hp will probably NOT be enough to plane a Jumbo. So, when one goes down, you are basically at displacement speeds since you can not get up. Then you have the prop sizing issues and the concerns of overreving them (one of them) if the other is out.

Basically it goes back to the idea of one large main, and a smaller kicker that pushes you at displacement speed to get home. Fairly interesting read if you have not seen it.

I wonder if 75hp or twin 90's would get you what you wanted, but I think 60 hp will be anemic.

You going 22 or 24 or realllly long at 26'??
 
Tod,
I was thinking about your question today and was reminded of this article by Tony Athens on Inboard Diesel engine life.
I think most of what is said in the article is directly applicable to the outboard side and maybe even more so. The two stroke and four stroke motors on outboards are called Hand Grenades by commercial diesel mechanics. So are the high output motors sold to the recreational sector of the marine inboard market.
"Performance is King", I just like my performance in hours not top speed, but I'm not a CO or Coastie trying to run to a rescue.
I think the Semi V of the Tolman is going to be very similar to many existing hulls in glass and so an OEM Engine Tech Assistant should be able to get you close with the power and torque charts once you get an idea of your hull loading and weight distribution.
The big question, as a builder, you have to answer is what is the acceptable performance goal you are setting, speed wise, and then you will work from there with the HP required calculations.
I could live quite well with a pair of 60's on a boat to almost 30 feet, but I may have a very different top speed requirement than the next guy. (I am cheep when it comes to recreation, so speed is low on my list)
If planning is important than the math is going to have to be done on the required min. to get her out of the hole. And then for the sake of longevity the extra cushion will be figured in so the motors can be run backed off at a sane RPM that will keep stuff form flying out the side of the block.
I have a few guys I know who would be helpful on the design/engineering side and the outboard/mechanical side. I plan on asking them some questions.
Give me a call so I can get some hull and weight info to get them in the ballpark.
 
I have a couple of things I would like to mention. The first is that it is almost certain that a single 60hp will not plane a larger Tolman skiff and will probably not push it past 10 knots, which a kicker motor would just about push the boat at that speed if not pushing against the current. However, if you are out in any kind of strong current and have to come in on one engine against the current (especially if you are 20 plus miles off shore) it would take DAYS to get in on a kicker motor, but the larger secondary engine would get you in much much quicker when fighting a strong current. Your not saving anything (except maybe $500) when going with a large main/small kicker setup vs. small twins. Small twins are lighter weight, more effecient, and quieter than a larger main.

As for the inboard diesel...of course it is going to have a longer life than a high output compact outboard motor. However, how much money do you want to spend? A small volvo diesel package with outdrive will run you about $20,000.....and you still only have one engine. My belief is that a outboard will run as many hours as you want as long as you USE IT and maintain it! The biggest killer to a boat engine, as i'm sure many of you know, is that it just sits and is not used. At my previous job, we maintained a commercial fishing boat that had twin Yamaha 115hp 4 strokes with over 8,000 hours on them (at the time I left the job) and it was just getting its first valve adjustment at that service interval. That is more than the typical engine life of a high-reving marine diesel engine, and those motors are still running strong.
 
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Sean,
I wasnt trying to sway Tod into using a diesel, just making the comparison to market perception as to life expectancy. (What I like and what Tod likes dosnt matter) Tony makes the case very well for running engines at about 30% duty ratting and expecting v. long service life, with proper maint. of all block externals. If you have the money, run the thing at the pin or 200 off and take your chances.
The part I think is most important is to set the operating goals so the numbers can be cranked and not just a flat out guess on buying two expensive motors and seeing how it goes. If two 60's require all they have to get Tod the speed he needs he may not get the life many think a motor should give. (Is this going to be run like a SAFE Boat or a Moose Boat for homeland defense? or cruise out to the clam flat and fish ground with family on board)

I dont feel a planning ride home is required in a one engine failure personaly, (I just want to get home on my own without a tow), but the handling advantages of twin engines for everyday use compared to a single with kicker, esp if the boat is built with a cabin FWD, in the wind and current will be very useful to the operator. (Privateer or Parker)
Some guys are OK with 11 kts. others will only be happy with 35. Each has dif. motor demands and will have diff. service life issues.
My fav boat is a steel hull dragger that makes 8 kts on a 4 cyl Detroit. Second set of pistons and bearings in 19 yrs. But you dont zip out to anywhere, you get there when you get there, thru anything.
 
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