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