hydrofoil basics - Help !

[ob1jeeper]

Am looking to add a hydrofoil to my 24ft CC Mako, with Johnson 235, because it's sluggish out of the hole (especially so when fully loaded). Already has trim tabs, which just make it MORE difficult to get on plane when "trimmed down"... so far the BEST trick I've found, is to trim BOTH motor & tabs WAY up, rev the Wee out of it, then slowly start trimming down the motor And the tabs, as it gains speed...<br /><br />I had good experience on my last boat with the doel fins, but my local OMC dealer suggested the Sport SE-300 would be a better choice.<br /><br />Started to put it on this evening, but discovered that it doesn't seem to fit very well, as the main mody of this thing sits WAY aft of the prop !!! Not at all like I remember the doel fins, and the specific instructions to NOT place them too far aft...<br /><br />In order to get the rear-most bolts to have more than 1/4" to the back edge of the cav plate, I'm going to have to modify this unit (the instructions say I can "notch it as much as 3/4"), but this seems out of whack, as I always thought the main body of the fin (and/or cav plate) should be pretty much over the prop rear face to have much effect on cavitation...<br /><br />Any thoughts or experiences to share?<br /><br />Thanx, Obiwan...

 

[DJ]

Re: hydrofoil basics - Help !

ob1,<br /><br />Can't help you with that brand of foil. However, I believe DHadley can, he'll be along soon.<br /><br />Are you sure you're propped right?<br /><br />I know the Mako is a heavy boat, but it should pop up relatively quickly.

 

[ob1jeeper]

Re: hydrofoil basics - Help !

Djohns, Thanx for the reply...<br />Have been trying a variety of props, etc, to see what works best at all of the various elevation lakes I boat at, and have a virtual "trunk full" of differing pitch props for this unit that I'm working on sorting out which is better for what lake. In desperation, I even broke down and bought of one of the $$ Land & Sea variable pitch units, which I'm hoping to try out pretty soon...<br /><br />But to answer your question... Yes props make a HUGE difference, as I can make it launch better with a tighter screw, but then it looses a BUNCH on top end...<br /><br />On my last boat, the hydrofoils were a BIG help in compensating for some of the power loss, due to altitude changes. So much so, that I was able to reduce to two basic props for the extremes of altitude differences (rather than the 4 or 5 props I drug around prior to the fins...)<br /><br />My main goal is to try to understand this Sport SE-300 a little better, before I commit to drilling holes in the cav plate, that I have to weld shut later.<br /><br />Any and ALL thoughts and experiences are welcomed... I'd like to make as informed a decision before dirlling holes a possible...<br /><br />Thanx again, Obiwan

 

[JB]

Re: hydrofoil basics - Help !

Howdy, Obiwan.<br /><br />I agree with your Dealer on the SE Sport 300. I use one and find it very satisfactory.<br /><br />You didn't mention what effect on WOT rpm the different props have.<br /><br />I am wondering if there is a problem with your hull, weight distribution or engine output.<br /><br />Your description of trimming out to drive the stern down being necessary to get the bow up suggests a bow-heavy boat, too much hull drag or a weak engine.<br /><br />I don't know if that will help, but it is my thoughts.<br /><br />Good luck.

 

[ob1jeeper]

Re: hydrofoil basics - Help !

JB,<br />Thanx for the input... At a 235 hp (in 1983 hp #'s ) This boat is indeed marginally powered for what I'm using it for... Sadly, the correction for that is WAY $$$, so I'm trying to "make do" with the available power.<br /><br />At sea level, (and up to 1500-1800 ft above), AND with three abord and 1/2 tank (~60gal) fuel, it planes out pretty well with a 17 pitch 3-blade stainless, and a top speed of ~45 mph.<br /><br />However, when I load it with a full tank (122 gal) and 5 "full-sized" adults, it takes abit more creativity to get that 17 pitch prop to push it onto plane. When it finally does get up, it still tops out near mid 40's.<br /><br />NOW comes the bad news... When I try to go to 3800-4000 ft elevation lakes (Lake Powell for instance), so far, the only real cure for the planing issue (when loaded) has been a 13 pitch prop, which jumps it up, but just holds it on plane at near max rated RPMs (5400) with speeds in the low 20's.<br /><br />Of course, reducing fuel load or passengersis a BIG boost, and I'm becoming more aware that this boat NEEDS more like 300 hp, but at the moment it is not practical due to $$$...<br /><br />So... I'm back to trying to do a little research to see what experiences with the fins are, so I can try to make a more informed decison about which one to use...<br /><br />I could use BOTH "how good X, Y, or Z works" comments, and any thoughts, and comments about durability issues, as placing this thing so far back on the cav plate has me a bit concerned with cav plate durability...<br /><br />Thanx again, Obiwan<br /><br />PS: motor JUST overhauled due to fried #6 piston... so far, so good... 5 hours on the motor, and no more "melt-downs" yet...