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Old 14 June 2014, 15:24   #1
DGS
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Country: UK - England
Town: Southampton
Make: Honwave T40
Length: 4m +
Engine: Honda BF20
Join Date: May 2011
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2.8 sib upgrade 4hp to 7.5/8hp worth it?

Hi I have a 2.8m sib with inflatable keel & high pressure floor with an old but reliable Mariner 4hp. It's very noisy & quite slow so I've been looking at upgrading to a 7.5hp or 8hp (that's the max rated for the sib). I've found a Evinrude 7.5hp for sale but was wondering if it would make that much difference to performance - I'd like to plane with me & my 10 yr old (total weight ~18 stone combined)? Thanks for any advice!
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Old 14 June 2014, 16:12   #2
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Country: UK - Wales
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Make: ribtec 3m
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Quote:
Originally Posted by DGS View Post
Hi I have a 2.8m sib with inflatable keel & high pressure floor with an old but reliable Mariner 4hp. It's very noisy & quite slow so I've been looking at upgrading to a 7.5hp or 8hp (that's the max rated for the sib). I've found a Evinrude 7.5hp for sale but was wondering if it would make that much difference to performance - I'd like to plane with me & my 10 yr old (total weight ~18 stone combined)? Thanks for any advice!
I had a 2.75m sib with inflatable keel, I started with a merc 4.5hp, It was ok but wouldn't plane I then got 6hp Johnson (1983) that would plane with me alone and I got around at 10-14mph (14 stone), I then got a 8hp evinrude (1986) that would just get me (14 stone) and my 14yo (6.5 stone ish) on the plane, I would say you will be ok as long as the engine is running at peak performace, I love johnson outboards thay are so easy to work on and parts are easey to get hold of
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Old 15 June 2014, 15:56   #3
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Country: UK - England
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Engine: Tohatsu 25hp
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Hi, I had the sunsport 270 V airdeck rated for 8hp,,,,, started with a late 70s yam 6hp was in good nick. Would only plane with my self in.

Then got a 80s merc 9.8,,,,, changed the boat 100%. A fraction over rated on paper,,, 9.8 at the time will have been calculated at the crank and not at the prop as now. Plane with me, wife and daughter in. Then got hold of a late merc 15hp,,,,. Well over rated,,, but good fun.

A 7.5 or 8hp will make a difference from your 4hp. Once on the plane you can drop the revs down and probably use less fuel than the 4hp at WOT.

It can get addictive, now have a 380 aerotec use either the merc 15hp or Johnson 30hp.

Happy boating.
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Old 23 June 2014, 17:58   #4
DGS
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Country: UK - England
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Hi - I bought the Evinrude 7.5 & it's so much more fun! It gets on the plane really quickly & is definitely quieter & smoother (probably due to 2 cylinders vrs 1 on the old Mariner 4hp). Also, it's no heavier than the old Mariner - it only weighs 26kg. The only thing I'd like to change is that the cowling is a bit scruffy - can you respray it (if so what paint do you use) & can you get replacement decals? Thanks
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Old 23 June 2014, 18:49   #5
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Glad it does what you want. Your right about the 2 cylinders,,,, less vibration, balance each other out.

Yes you can repaint the cowling and buy replacement decals, decal prices vary,,,,,, original or copies.

Painting is like car body work, the more time you put in before the paint the better the finish (youtube it if you need info). Car paints should do the job (aerosol) get the same products, primer, colour and lacquer if you need it.
Top coat with a clear lacquer that is petrol proof or you may find all your hard work come off. (you could do a sample on some thing else with your paint and see if the paint reacts with the petrol).

Good luck.
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Old 24 June 2014, 04:01   #6
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i had a 2.85 zodiac, with 2 people (180kg combined) and 12l of fuel we would plane on flat days if the mrs st right up the front. we had an 8hp johnson. by myself it was harder as i didnt have a tiller extension, so slowly i got on the plane.
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