From 2x60 2st to 1x100 4st

[ed_dash]

Hi

Im thinking of replacing my twin 60's and have seen a yammie 100hp 4 stroke for sale at a reasonable price. At the moment i get around 38kts from the twin 60's would i be seeing a similar performance from the single 100?

I have read on here that twin is roughly 1.5 the power so that would be a 90 2 stroke, but has anyone actually gone from twin 2 strokes to single 4 stroke?

[Downhilldai]

Saw that one myself and got me wondering....
I reckon it will be great on your RIB.

[9D280]

Ah, the old "1.5X" chestnut...... I have a thory about that approximation! In short it is more accrate at the huge HP end of the scale - i.e twin 150s are not the same as a single 300. Down at the other end of the scale the speeds are less, so the "double drag" theory is les pronounced amongst other things.

Is yours the one I saw on here a while ago with the twin Clamshells? If so, I suspect you may not get much of a diffference in performance. The clamshell clocks in around the 83 KG mark, so your current weight is approx 166Kg for the pair. Honda don't do a 100 any more, so I have used the two either side, not knowing which one the 100 was based on. The 90 is 172KG , the 115 is 220Kg Sothere's at least 6 KG weight gain before you've even bought your Aux!

Then the gearbox - the clamshell 60 has a 'box that is at the top of it's power sharing group, and is on a par size wise (and theregore drag wise) with most 30 HP engines on the market these days.

So, based on comparing a guestimate of the Honda with a picture I can't even remmember if it's your boat or not, I personally woud be giving it some serious thought to sticking with the twins. If yours aren't clamshells, I'd still be doing a similar comparison, especially if the 100 of yore is what become the 115......

[Downhilldai]

Originally Posted by 9D280

Ah, the old "1.5X" chestnut...... I have a thory about that approximation! In short it is more accrate at the huge HP end of the scale - i.e twin 150s are not the same as a single 300. Down at the other end of the scale the speeds are less, so the "double drag" theory is les pronounced amongst other things.

Is yours the one I saw on here a while ago with the twin Clamshells? If so, I suspect you may not get much of a diffference in performance. The clamshell clocks in around the 83 KG mark, so your current weight is approx 166Kg for the pair. Honda don't do a 100 any more, so I have used the two either side, not knowing which one the 100 was based on. The 90 is 172KG , the 115 is 220Kg Sothere's at least 6 KG weight gain before you've even bought your Aux!

Then the gearbox - the clamshell 60 has a 'box that is at the top of it's power sharing group, and is on a par size wise (and theregore drag wise) with most 30 HP engines on the market these days.

So, based on comparing a guestimate of the Honda with a picture I can't even remmember if it's your boat or not, I personally woud be giving it some serious thought to sticking with the twins. If yours aren't clamshells, I'd still be doing a similar comparison, especially if the 100 of yore is what become the 115......

It's not a Honda, but a Yam F100, which weighs 170kg.

[9D280]

Originally Posted by Downhilldai

It's not a Honda, but a Yam F100, which weighs 170kg.

D@mn Monday mornings.........

It's still 4Kg Heavier if Ed's 60s are Clamshells. (probably more if that''s Dry weight)

[ed_dash]

Dont think they are the clamshells, late 90's models, but their weights are 94kg each so id save 18kg by getting the 100. Not a huge amount but still a small saving.

Im currently happy with the performance i have, just looking to see if i can improve without spending much money and any fuel savings after changing to a 4 stroke would be a bonus.

[gotchiguy]

Originally Posted by ed_dash

Im currently happy with the performance i have, just looking to see if i can improve without spending much money and any fuel savings after changing to a 4 stroke would be a bonus.

Why not get a replacement single modern two-stroke? Significantly less weight, so better performance, and consumes just as insignificant amount of fuel as a four-stroke. More power also, a single 100 4s is inherently less powerful than an equivalently powerful 2s of the same capacity

[Downhilldai]

Originally Posted by gotchiguy

Why not get a replacement single modern two-stroke? Significantly less weight...

What did you have in mind?

Originally Posted by gotchiguy

More power also, a single 100 4s is inherently less powerful than an equivalently powerful 2s of the same capacity

[ed_dash]

Only thinking of the 100 4stroke because there is one for sale at a good price. I think ideally i want a 115 or similar but if the price is right and the engine is good i have nothing against etecs, Opti's or 4 strokes.

[Downhilldai]

Originally Posted by ed_dash

Only thinking of the 100 4stroke because there is one for sale at a good price. I think ideally i want a 115 or similar but if the price is right and the engine is good i have nothing against etecs, Opti's or 4 strokes.

Stop spoiling the fun

[Simon B]

Hold out for the F115, the F100 I think was never fuel injected or ECU controlled just carbs. The F115 should be more economi with a modest hp gain for not that much extra weight. It's only a bragain if you were shopping for it to start with.

[ed_dash]

Weight wise, the yammie 100 is 170, the etec 115 is 170, the opti's are 170, so there isnt much difference and all around the 188 i have on the back now.

Power wise, isnt a 100hp always a 100hp whether its 2 stroke or 4 stroke? Surely its just the torque that differs?

If i were buying new that would be a completely different argument, and my opinions on type would differ and i think id probably join the etec club.

Out of interest, anyone know why does a 150 verado costs nearly 4k more than a 150 Opti?

[9D280]

And the fuel economy of a 4-stroke only significantly comes into play when you spend a lot of time at low revs...... Bottom line is if you want 100 HP, you need to burn a certain amount of fuel, coz the laws of nature & themal efficienncy kick in.


Ed,
You don't have Clamshells if they clock in at 114KG each! (Clamshell is the "street" name for the old Merc / Mariner lumps with a wraparound cowl). The early ones had their problems, (as I have since demonstrated! ) but they were remarkably light for the horsepower.

[Downhilldai]

Originally Posted by ed_dash

Weight wise, the yammie 100 is 170, the etec 115 is 170, the opti's are 170, so there isnt much difference and all around the 188 i have on the back now.

Power wise, isnt a 100hp always a 100hp whether its 2 stroke or 4 stroke? Surely its just the torque that differs?

Now, you're really spoiling the fun.

Originally Posted by ed_dash

Out of interest, anyone know why does a 150 verado costs nearly 4k more than a 150 Opti?

I think it's on the theory of 'if you can afford to fuel it, you can afford £4k extra to buy it'

[ed_dash]

not that i like disagreeing with the vast knowledge on here, but mine have a weight of 94kg stamped on the id plates along with the serial numbers, even if thats before the oil tank is filled, that is only a few kg.

Here is a pic i found on here:

http://www.boatsplus.com.au/mariner-...e/prod_54.html

i dont have the bigfoot gearbox thats on the spec sheet so the weight wou;d be a bit less.

[Pikey Dave]

Originally Posted by ed_dash

Power wise, isnt a 100hp always a 100hp whether its 2 stroke or 4 stroke? Surely its just the torque that differs?

And torque is everything
Torque gets you on the plane
Torque pulls up the skier
Torque is the kick in the pants when you bury the throttle(s)
Torque gets you up the face of that fkin big wave
Torque is king

[9D280]

Originally Posted by ed_dash

not that i like disagreeing with the vast knowledge on here, but mine have a weight of 94kg stamped on the id plates

And that is why rules of thumb have their place, but you just can't beat good old reality!

[gotchiguy]

Originally Posted by Downhilldai

You know very well that on the whole a 2/ rated to 100 will produce more power that a 4/ rated to the same power output, not only in terms of torque but horsepower too.

Obviously this is a generalisation (especially in the case of horsepower), but the basic concept of the two stroke motor results in greater power over a 4/ of the same ccs. The E-tec 130 for instance, although undoubtably one of the weaker engines in the e-tec stable, will provide significantly greater power than the weak Suzuki DF140 (128hp what). However there is no way it could keep up with the big block DF150's torque. In a marine application, torque (as played upon by Evinrude and Pikey Dave) is the biggest player.

I am a firm advocate for 2/ DI, but even I know that in many applications 4 can be better than 2. The reason I tried to make a point here was because the OP was worried about the performance aspect compared to his current engines.

To answer the OP's question, I agree with 9D280, just replace the twins with modern 2/ and save the hassle of all the work involved in changing to a single

I see no point in trying to explain my point further, since I know you believe in the same principles, seeing as your two boats are both 2/.

[Downhilldai]

Originally Posted by gotchiguy

You know very well that on the whole a 2/ rated to 100 will produce more power that a 4/ rated to the same power output

No, it won't.

Originally Posted by gotchiguy

The E-tec 130 for instance, although undoubtably one of the weaker engines in the e-tec stable, will provide significantly greater power than the weak Suzuki DF140 (128hp what).

No, it won't.
(unless the 128hp claims are accurate and you consider 2hp to be significant)

Originally Posted by gotchiguy

I know you believe in the same principles

No, I don't

Originally Posted by gotchiguy

your two boats are both 2/.

No, they're not.

[gotchiguy]

Normally I would argue back, but unfortunately I'm too busy. Controlled Assessment and all that

Onwards Blackpig!!