16 replies to this topic

[thumper]

in an attempt to gain an extra few knots(wishful thinking) i have polished the hull in anticipation for the warmer weather and the new season, dont know if anyone has applied seaslide yet but after last season my hull was a little dirty so i have polished it several times with auto-glym and buffed it- i guess it cant do any harm?

seaslide claims it reduces friction between the hull and water - so i guess a silicon based polish will do the same - it feels slippery! - have to wait and see.

[Kevin Leclair]

Sounds like a good idea, let us know if you noticed any difference.

[thumper]

it worked -

after polishing my hull with auto-glym and buffing it several times - managed about 67mph at weekend in less than ideal conditions - 2 persons on board and full tank of fuel
so i will add a few more coats of polish

[thumper]

out with a buddy this weekend who is a photographer and took some pretty cool photos heres one will put rest in gallery if i can work out how to doit

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[thumper]

ok gallery doesnt like my pics so i will post the here - they are too big???????

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[thumper]

another

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[thumper]

another

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[Yuji]

67mph!...is that on the dreamo-meter or do you have GPS? I wish someone would try out that seaslide stuff and get back to us with some results.

I'm going to true my rideplate by filling in the holes and smoothing out the gaps between hull and rideplate...should be good for small increase in mph. I'm also waiting for a new trim tab from BRP, in prototype stages right now. The planing time on this c180 is horrible not to mention porpoising.

I'm going to have this thing flying by this summer if it kills me

[fialoe]

Looks great, well done.

[thumper]

no 67 was gps alright it was 66.8 but who cares - one major difference we have over here that i dont believe you have is very high octane fuel - super plus unleaded - this fuel seems to have a marked effect on high performance engines its at least 98 octane, and the polished hull really did make a difference.

[Yuji]

wow! thats some insane speed, especially considering we have the same powerplants and I only get 47mph I guess thats what an additional 600lbs and different hull will get ya'

What was your top speed before the polish job?

[thumper]

i think my top speed was about 63mph so it really made a difference - mind you i did put 3 layers of auto-glym on the hull

[tda3]

Yo Thumper - long time no chat.

Wow.....67 on GPS. Most impressive. I suspect you'll be wearing your arm out polishing that thing though seeings how that polish will wear off rather quickly. Especially if you're boating in salt water which has more mineral content.

Probably the easiest way to increase speed is by decreasing the wetted area and/or breaking the adhesion that occurs when water is passed over the surface of a hull. That's why you see high peformance boats having so-called stepped hulls and notched transoms. The "steps" in the hull create turbulence which translates into tiny air bubbles that break the adhesion resulting in the hull running "free'er". IMHO coatings are mostly snake oil. I've been to many types of boat races from Offshore to Hydro's and have never seen anyone applying some miracle slipery stuff to a hull. What they will do is blueprint the bottom (making sure the hull is symetrical and the bottom contours are consistent laterally and longitudinally) and polish the surface of the hull. As for wetted area, the rule used to be 1" of wetted surface (measured from transom going forward) for every foot of length. IOW, if you have an 18' boat, only 18" of the hull should be touching the water for max speed.

What I think Thumper has done with all his buffing is to smooth out the imperfections in the fiberglass surface. So in essence, it's the smoothness of the hull and not the stuff he used that's rresponsible for the speed increase. When you have thousands of pits and nicks and whatever in your hull, you're adding drag.

That's all for today's lesson. Class dismissed. LMAO

Tom

[thumper]

i have checked the hull and afetr approx 8 hours on the water its still glass smooth to the touch, before i polished it it was a little sticky for want of a better description, there were no nicks or dents though, i will say the 66.8mph run was the initial run after the hull was polished i couldnt testify that it maintained this all day - so you may well be correct tom. on the stepped hull theory, i have often wondered why seadoo dont introduce a stepped hull and although thay may doo in the future - or they may have on some models i am unfamilair with - i was wondering whether introducing air under the hull may cause impeller ventilation? - an interesting debate - but i will continue to polish my hull - i would also say that despite the increase in speed the boat still handled superbly - which is the main thing whilst striving for extra speed.

[thumper]

tom - as for the wet bits - heres a photo of me passing a buddy who took some pics for me - i am doing about 50mph - there is aprroximately two thirds of the hull in the water, the water was very calm and flat, i guess with jet boats the 'suction' created by the pump inlet keeps the hull glued to the water, what this photo also showed me was that i should be polishing a little more of the hull forward of where i had previously, ..................

i will also look to polish my head just to squeeze out a couple more knots

high speed - low drag haircuts are a amjor factor i am sure

watch out for our next photo shoot - when my buddy comes next we are doing an underwater video of start up and drive by to see the pump in action - we are both divers and decided to do this in 6-20ft of water, and also in 3ft of water to see if the pump really does pick up sand etc from the bottom at this depth -

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[tda3]

In no way do I mean for this to be argumentative.....

I still contend that what you did with the polishing was to increase the suface finish of the hull thereby reducing drag. IOW, you made the surface "shiny'er" just like polishing metal. Normal aluminum (sorry - that's al-you-min-ee-um to you )sheet is rather shiny from the mill yet will corrode quite easily. However, if polished to a very high state, it can withstand corrosion without any coating. Technically, surface finish is expressed in RMS terms - the larger the number, the high the surface finish.

As for stepped or ventilated hulls......there's two camps - those who feel they're the way to go and are safe and those who feel the handling can be dangerous and that other hull designs are more forgiving and have just as good turn of speed.

Steve Stepp and Reggie Fountain both have a very long and very successful history of racing in outboards, formula, hydros, offshore, etc. Steve feels that vetilated hulls, when driven close to the limits, are ill handling and not for the average boater. In the hands of a pro they're fine, but they still have a propensity for spinning out or rolling over in turns that are not executed properly. Steve contends that his pad keel design is just as fast but without the evils of the ventilated hull.

Now Reggie, who all but invented the ventilated hull, feels ventilated hulls are safe in the hands of any boater and that the ventilated hull achieves it's speed more efficiently. Reggie (as well as Steve), has set many UIM records so the numbers should speak for themselves. However, numbers don't tell anything about a boat's handling when running - especially flat out. I'd love to be in a room with these two guys debating the subject. It would be most informative and entertaining.

As for how a ventilated hull would affect the intake of a jet pump - i.e lead to cavitation issues.....I suspect there wouldn't be any issues. The steps are typically well outboard of the hull's centerline and are the most prominent at the hull's chine. Since the hull is displacing the water (even when on plane), the flow of water off the hull is outward as witnessed by a boats' wake. It's possible that SeaDoo knows about the handling ills of ventilated hulls and just don't want to deal with the potential liability issues.

In next weeks lesson we'll cover chine walk and how it leads to boat seat butt suction.

Tom

[thumper]

interesting discussion - i do take your point about the polished hull - and i hadnt realised that the stepped part of the hull was not all the way to the kiel - i guess various designs will be different - i have been in a mono stepped hull and cornering was difficult at speed - it felt very twitchy - like a very high powered rear wheel drive car, the back end kept skipping out causing dramatic oversteer - which felt rather unerving, doos however dont seem to over or under steer despite the speed you are doing - they feel more like high powered four wheel drives - very confident control at speed in a straight line and tight high speed turns, or at least thats how the sportster handles, anyway we digress, you are obviously well versed in the subject tom and please dont feel that you are being argumentative, i appreciate the oppurtunity to learn something - whichg i great because the missus just thinks the forum is about swapping jokes and beer stories!
i would ask if you could explain some of your abbreviations - they are a little puzzling!