Best Engine Choice for 5.4 Searider?

[DM]

Originally Posted by Pikey Dave

I agree, but you didn't mention that initially, you highlighted the top end performance difference

I didn't highlight anything. I pointed out, that of two identical boats, the one with twins had a better top speed which goes against the accepted theory that a single of similar HP would be faster because of less drag.

[DM]

Originally Posted by Downhilldai

I quite fancy owning an SR5.1

We need a 'how long is your searider' thread.

Somethings not right

[colcreate]

Originally Posted by Downhilldai

I'd say around £600 - £700 each. Would suit an SR4 nicely and there's always guys resurrecting them.

The market for selling them as a pair would be limited.

Having seen the cr*ppy engines some people pay £700ish for without controls etc I think the condition of these would get nearer £800 they really are that good. IMHO

[Downhilldai]

Originally Posted by colcreate

Having seen the cr*ppy engines some people pay £700ish for without controls etc I think the condition of these would get nearer £800 they really are that good. IMHO

Give them a try on B&O or e-bay then.

They're 20ish years old, but look tidy enough, so you could get lucky.

[Pikey Dave]

Originally Posted by DM

I didn't highlight anything. I pointed out, that of two identical boats, the one with twins had a better top speed which goes against the accepted theory that a single of similar HP would be faster because of less drag.

er, but you weren't, you compared a 100 to 2x60 which if my schoolboy maths serves me correctly is 120hp. If you'd said 2x50 hp (100hp) was faster then you'd have had a better case. Without knowing the gearbox ratios, prop pitches & WOTs then the comparison is meaningless. By overpropping the twins & underpropping the single you could make the figures say anything you like. That's why the other factors (planing speed, holeshot etc) are important to get a useful comparison.

[TMB]

Originally Posted by colcreate

Wow, can't keep up with the responses to this one... need more beer!
Hmmm, really liked the idea of twins has anybody actually had any first hand experience with this set up? What if they were PTT would that sway opinion?

Obviously a single 90hp will thrash twin 40's but by how much.
Weight:
2 x 40 = 270lbs
1 x 90 = 260lbs but add on a 6hp backup??

Selva's, yes I like them but a lot don't which makes them silly cheap 2nd hand so I keep my eye out for them and pick them up for little money (think I have enough now though). I believe Yamaha have owned a minority share in Selva for years (four stroke Selva's are rebadged Yamaha).

Perhaps I need to buy another SR5.4's to compare.
Then I can have one with one with twin 40's to carry all the spares for the other Selva powered one!

How about this 90hp Yamaha on ebay http://cgi.ebay.co.uk/ws/eBayISAPI.d...m=170546379621 & video here:

£150 delivery from Lithuania is it worth the risk?

I have twin 40hp yammys on one of my seariders. Check my website gallery for pics. You will get 32knts tops, but they are great for redundancy. The boat will get 20 knts on one engine. The boat is maxed out with twin 40's (weight) I had 40kg gell coated into the front of the craft as it chine walked really bad. Great set up though.

[DM]

Originally Posted by Pikey Dave

er, but you weren't

Yes, I was

[chewy]

Originally Posted by Pikey Dave

er, but you weren't, you compared a 100 to 2x60 which if my schoolboy maths serves me correctly is 120hp. If you'd said 2x50 hp (100hp) was faster then you'd have had a better case. Without knowing the gearbox ratios, prop pitches & WOTs then the comparison is meaningless. By overpropping the twins & underpropping the single you could make the figures say anything you like. That's why the other factors (planing speed, holeshot etc) are important to get a useful comparison.

Yup, you could fit twins and only run one, that would really f*ck with your figures!

[colcreate]

Originally Posted by TMB

I have twin 40hp yammys on one of my seariders. Check my website gallery for pics. You will get 32knts tops, but they are great for redundancy. The boat will get 20 knts on one engine. The boat is maxed out with twin 40's (weight) I had 40kg gell coated into the front of the craft as it chine walked really bad. Great set up though.

I like it, and your website gallery is great.
30+knots is probably good enough for me. Chine walk is bad though I thought twins would improve stability. Does a 80/90hp single chine walk as bad, I hear 38 knots is possible?

[TMB]

Originally Posted by colcreate

I like it, and your website gallery is great.
30+knots is probably good enough for me. Chine walk is bad though I thought twins would improve stability. Does a 80/90hp single chine walk as bad, I hear 38 knots is possible?

Never had an issue with chime walking with my singles. I have one with a yammy 80 and one with yammy 90. They are pretty stable boats with singles as long as they are set up well. Once again it also depends on the prop you are opperating. SS or standard fit makes a difference. My boat did not enjoy the 18 pitch ss one I put on her lately. I think I have just sold my 2004 tohatsu 90. Shame, its sat on a good boat and they are good engines.

[colcreate]

Originally Posted by TMB

I have twin 40hp yammys on one of my seariders.

Looking closely at your twin engined transom it looks like you have set them down a good 1" or so below normal height. Doesn't this low setting tend to increase the chances of it falling on to the chines? Did you experiment with different setting to arrive at this?

[TMB]

Its hard to see on the photo's but the 40's are raised a couple of inches above the transom for perfect prop allignement with the chimes. (Yes I did have a play with them) Pain in the arse

[walruz]

One dive club I was with had a 5.4 with twin 40 mariners and she really didn't like carrying any weight. Personally a big single every time.

Ian

[Downhilldai]

Originally Posted by Downhilldai

Soozook DT90: not many of them around, but if you could find one, it would be a super motor on a SR5.4. It's a 60 deg V4, 1.5 litre, good on juice and bags of grunt. Basically a de-tuned DT100, produced in the mid to late '90s to replace the ageing DT85, before Soozook went all 4-stroke on us.

One here, only £1250 - cheap:

http://www.boatsandoutboards.co.uk/view/PAA14995

[PeterR]

Originally Posted by colcreate

Thanks DM, one vote for the twins then!
I wonder what insurers would say about overpowering a SR with the 115hp I know it's often done but could it be a problem?
Has anybody got true performance figures for a Yam90 5.4?

I,ve got a searider with a transome plate rated to 120hp.I think you will find its only military spec ones that have had the uprated plates Twin 40hp four strokes i have had for a year.Very quiet smooth and thought they were great.you loose though on fuel economy then range service costs heavey on the transom.Long shafts need to have the transom cut otherwise they cavitate badly and the water level is very close to cut out. 90hp yam is best like chewy has said .I have had 4 seariders two with yams and by far the best. Insurance for overrated engines or overweight.I contacted Porthcawl who i am with they said as long as the transome has been strenghtend they have no problem as modern fourstrokes are heavy. JSP,s 115 was scarey

[Rogue Wave]

Originally Posted by TMB

Its hard to see on the photo's but the 40's are raised a couple of inches above the transom for perfect prop allignement with the chimes.

That rings a bell

Yam 90 2 stroke followed by Toohotsu every time if new probably buy a TLDI 90. I understand that Yamaha are bringing out a new lightweight 4 stroke range with the 90 being of comparitive weight to the 90 2 stroke but it's probably about 82k

I Like twins on any boat so 40 s or 50's would be great

[9D280]

Twin vs single- here we go again........

The drag argument is going to take on a whole differnet angle at that kind of HP. two reasons -1) the 40s will have substantially smaller gearboxes & legs than the 90, so less frontal area. 2) the whole rig wil lbe travelling a lot slower (in the bigger picture) than something with 300 hanging on the back.

Now, drag through water is equivalent to approx the square of your speed and the cube of your frontal area. Net result - at that kind of HP the differnece is verging on negligible (as shown above).


Now, as has already been pointed out, with a single you need an aux. bang goes the diddy weight saving. Boat full of divers - what would you rather have? a 6Hp aux or a 40? Lack of PT? you just do what I did with my old Yam- go out & play with it for an afternoon - find the optimuim place for the pins.


In this case, I'd probably go with the twins.

As an aside, I bet if you looked around you could find a couple of suitable PT units to retro fit.

[piranha580]

Brand new Suzuki dt90.. Lightweight compared to some other 90's.. New streamlined gear casing .. Great economy...!!

[Downhilldai]

Originally Posted by piranha580

Brand new Suzuki dt90.. Lightweight compared to some other 90's.. New streamlined gear casing .. Great economy...!!

That would be a DF90

[piranha580]

Originally Posted by Downhilldai

That would be a DF90

Apologies you're dead right.. That was a typo on my end.. Damn iPhone !!! 