shetland 535 suntrip and old suzuki dt65, what would be the best prop?

[chestercheese]

hello, i've just restored an old shetland 535 suntrip, i've stuck a 1980's dt65hp longshaft on the back and using what i think is the standard prop, but when i took it out on sunday with 4big men, i could only reach a max of 12 knots at wot rpm was at about 3500, and could not get any more out of it, could anybody suggest what size prop would give me a higher speed? as 65hp is ment to be the max for my type of boat, and it will normally carry 4 men (16stone each) and about 50litres of fuel, spare 5hp outboard and fishing kit. when i was out i used 45litres of fuel, about 4.5hours, and only done about 8miles
many thanks dan, any help would be great

 

[steelespike]

Re: shetland 535 suntrip and old suzuki dt65, what would be the best prop?

We need prop size,Usually appears near the base of the blades or under the prop nut.
You'll have to help us on the shetland.Size, Style Glas or metal.
Intended to plane? Some pics would be great. A guess on the weight dry and fully setup loaded.
Would be good to have a lightly loaded rpm and speed.
At wot the 65 will use about 6.5 gallons per hour.Can you pin down the year of the motor?

 

[chestercheese]

Re: shetland 535 suntrip and old suzuki dt65, what would be the best prop?

Hello. I'm not sure on year of outboard as the plate is missing. But I'm sure its 1980. The shetland is 1979 fiberglass 18 foot. And its prob about just under 1ton when loaded. I will find out the prop size later. Hope this helps a little? I would like to get it up on the plane as there are some strong currents where we go and it did struggle a bit getting through.
Many thanks Dan

 

[steelespike]

Re: shetland 535 suntrip and old suzuki dt65, what would be the best prop?

My Suzuki info doesn't go back that far; but my research indicates a 65 should push 2000 lbs at about 29-30 mph.
4 "big men could be 1000 US pounds by themselves, The boat by itself probably over 1000 lbs dry weight.Motor about 220
then there is fuel, gear batteries etc. You still should plane with the right prop.I feel we will need a light load wot rpm and speed
to evaluate your setup.It does appear with a further check the Suzuki is about 180lbs.

 

[chestercheese]

Re: shetland 535 suntrip and old suzuki dt65, what would be the best prop?

Hello again. I checked the prop size and its 11 1/4 x 15
Is there any different size that would be better for my boat?
Many thanks and I look forward to hearing what you suggest

 

[chestercheese]

Re: shetland 535 suntrip and old suzuki dt65, what would be the best prop?

Hello again. I checked the prop size and its 11 1/4 x 15
Is there any different size that would be better for my boat?
Many thanks and I look forward to hearing what you suggest

would putting dol fins on make a difference?

 

[steelespike]

Re: shetland 535 suntrip and old suzuki dt65, what would be the best prop?

The15 is definately too much prop. It would be good if we could get the a wot rpm and speed with a light load so we can get it planed out. Your rpm is really low because the boat isn't planing.
Also is the boat intended to have a long shaft motor?
I'm thinking an 11" pitch.It could be too light but your better off light because you can throttle back to stay within limits.
Again a lightly loaded test run will help to pin down the prop size.
Usually fins are a bandaid over a poor setup.They can help in the right setup.
But also can create problems like strange steering too much boat in the water
extra drag. Something like smart tabs carefully applied can be a big help.