Tranona
Well-known member
The extra 1" diameter would change revs by around 250, so a 14*9 should enable you to achieve 2500 and cruise at under 2000. However it will only give you about 0.5 of a knot of extra speed in flat water.
MAXI 84 , HOW FAST SHE IS?
- Thread starter fruk
- Start date
charles_reed
Active member
Down hill with a following wind - I guess quite easy - but the shaking from that rear door was considerable @ anything over 60mph.
Eunnily enough my 46-year old son in Finland was reminiscing about the Maxi we had in Reading (about 1977). Of course everyone on this site has a one-track (boat) mind and automatically thought of the Pelle Peterson, flush-decked masthead rig.
I only sailed one once - a sluggish sailer unless off wind in Bf4-5 and achieving about 6 knots under power. But it packed a lot of fairly comfortable accomodation into a shortish hull, and was one of a vast range of yachts ranging from 6.8 -10.5m.
Of all of them I guess the 95 was the most popular (and its residual value now bears that out).
vasant
Member
thanks all guys for the interest.
However the issue is not that i am lacking half a knot or so.
With this config i should reach one way or another apprx 6,5 knts. I can barely get more than 5. I checked also here http://www.vicprop.com/displacement_size.php?action=calculate and the overall setup ( power, prop size, gear ratio) should bring me to more than 6 knts easily. Boat is just out from the yard, so polished !! just wondering.......
sailorman
Well-known member
I very much doubt you can attain 6.5 kts, what is her LWL
vasant
Member
BabaYaga
Well-known member
How fast under sail? According to the Swedish handicap system SRS the value for Maxi 84 is 1.045.
Which makes her a trifle slower than HR 29 and Shipman 28 and quite a bit faster than the Vega at 1.001 (to pick a few boats of similar size that might be familiar in the UK).
BTW Maxi 77 has the same handicap value, 1.045.
Which makes her a trifle slower than HR 29 and Shipman 28 and quite a bit faster than the Vega at 1.001 (to pick a few boats of similar size that might be familiar in the UK).
BTW Maxi 77 has the same handicap value, 1.045.
Tranona
Well-known member
That calculator gives a maximum potential speed of 5.9 (against a theoretical 6.4) with your 13hp, very similar to the 5.8 that the Propcalc programme I used gave. To get 6.4 it says you need 17hp, which is what I suggested - confirmed by the calculation I did using a Volvo 2002/120 drive (18hp). Your calculator suggested a 14.8*8.8, but your 15*19 is just a bit too big, which is why you can only get 2300 revs.
You really are working on narrow margins, and changing to a 14*8 will get the speed up a bit (and the revs) but doubt in practice it will get much higher than 5.5.
vasant
Member
Hey its not 15x19 of course!! that would be steep indeed. I have 15x9 which is actualy close to the proposal above.
But yes you are right I made some calculations with propcalc and come also to 5.7 knts.
Ok in that case i have to use my sails a bit more to be faster.......
alahol2
Well-known member
Don't forget also that a boat in cruising trim with full tanks and all the gubbins on board is a lot heavier than the brochure says. Mine (similar size) is 500Kg up on the brochure displacement. Brochure 3,400Kg, Actual 3,900Kg (according to crane load cell).
Tranona
Well-known member
Hey its not 15x19 of course!! that would be steep indeed. I have 15x9 which is actualy close to the proposal above.
But yes you are right I made some calculations with propcalc and come also to 5.7 knts.
Ok in that case i have to use my sails a bit more to be faster.......
Sorry about the extra digit creeping in - my big digits again!
maxi
Member
Re Joepak, I have re-engined my Maxi 95 with a Beta & after now 1000hours am still delighted with it.
As regards your air vents I am assuming that they are the same as on the 95, stainless steel domes with a flat perforated top and with plastic open/close mushrooms within the domes (originally called Aeolian). If so, I managed to find new ones at trade price (cica£7.90) from Plastimo, just threw away the plastic domes that now replace the ss versions. easy job & very worthwhile at the trade price.
As regards your air vents I am assuming that they are the same as on the 95, stainless steel domes with a flat perforated top and with plastic open/close mushrooms within the domes (originally called Aeolian). If so, I managed to find new ones at trade price (cica£7.90) from Plastimo, just threw away the plastic domes that now replace the ss versions. easy job & very worthwhile at the trade price.
Viking
New member
Just catching up! The VP 2030 28hp is lighter more modern, then the old MD7B 17hp I had in my old 84. No large fly-wheel! Hope you've done the improvements by now? :0)
vasant
Member
Now i found an old test from some swedish magazine where the theoretical speed for the md7a setup has been defined to 5,8 knts.
sailorman
Well-known member
That is more realistic
Frankklose
Member
I owned a Maxi84 for several years. My friend had a Maxi77 with an inboard Diesel. The Maxi84 and Maxi77 are equal on speed, but dont forget the Maxi77 is very fast for her length.
vasant
Member
Hi all,
Here i am again in this mythical thread. Two seasons passed so i had time to investigate and observe things on the boat. I am pretty confident that something is not as should here, maybe my perception but i have been reading also other MAxi relevant posts and it seems i am pretty alone with the issue here.
SO i recap:
Engine MD7A (13hp) with 110s (1.66:1 ratio) saildrive and 15x9 propeller. the older worn 14x8 had pretty similar behvior as the 15x9.
When the boat is out from the yard that is polished and without any fouling it will reach 4.9 knots at approx 2300rpm (adding more rpm doesnt seem to hve any impact, 2600 is max). TAken into account the ideal conditions i claim this is little. No smoke or overheating at the engine part no problem in achieving the desired revs. NOw after some months with some light fouling on the prop and still very clean boat in very light chop the speed cannot even reach 4 knts. In flat conditions it will be max 4.5. I still cannot think this is normal, the boat is also not loaded the water tank of approx 80 litres is not even half foul.
I would really be interested to hear other people experience with this setup.
Here i am again in this mythical thread. Two seasons passed so i had time to investigate and observe things on the boat. I am pretty confident that something is not as should here, maybe my perception but i have been reading also other MAxi relevant posts and it seems i am pretty alone with the issue here.
SO i recap:
Engine MD7A (13hp) with 110s (1.66:1 ratio) saildrive and 15x9 propeller. the older worn 14x8 had pretty similar behvior as the 15x9.
When the boat is out from the yard that is polished and without any fouling it will reach 4.9 knots at approx 2300rpm (adding more rpm doesnt seem to hve any impact, 2600 is max). TAken into account the ideal conditions i claim this is little. No smoke or overheating at the engine part no problem in achieving the desired revs. NOw after some months with some light fouling on the prop and still very clean boat in very light chop the speed cannot even reach 4 knts. In flat conditions it will be max 4.5. I still cannot think this is normal, the boat is also not loaded the water tank of approx 80 litres is not even half foul.
I would really be interested to hear other people experience with this setup.
PotatoNavigator
Member
"And Vasant raised the Thread and will also raise us up by his power."
anoccasionalyachtsman
Well-known member
vasant, how are you measuring the speed? From your description the prop match is about right, and with a clean hull you should be going faster. (With ref to fouling, I once established that weed costs 1% of max speed per week of growth - in the Solent and measured over 4-6 week periods on a 40ft boat).
Potato Navigator, it wasn't so long ago that anybody asking a repeat question on a forum got howled down with outraged cries of 'do a search'. Now it seems that the op shouldn't even revive his own thread? How times have changed.
Potato Navigator, it wasn't so long ago that anybody asking a repeat question on a forum got howled down with outraged cries of 'do a search'. Now it seems that the op shouldn't even revive his own thread? How times have changed.
PotatoNavigator
Member
Occasional Yachtsman, I think you've misunderstood my post, I have no issue with threads being revived where relevant. It's especially good to see people revive their own threads with a follow up, such as this; there are too many threads on here about people starting new projects or voyages that we get invested in but then never find out what happened.
vasant
Member
always with a some GPS SW running on the phone.
