Very small porpoising effect Black Brant II

Steve Talbot

Steve Talbot

Member
As the title leads , on GPS the speed runs 24.75 Mph , these seems to be a ghost porpoise that will happen and quit, history is 25 HP Mercury 2 stroke, I adjusted the transom height to correct water coming over the end. The boat feels like it is right on the edge of sliding out but does not, I think it is adjusted about as good as I can do it,the porpoising is so small and goes away, it's like it has a small rpm range to happen and the its gone, was wondering if this is normal or has someone else went down this path, I'm not chasing this it's more of a information seeking post.
for the record, the 6 Gallon fuel tank is forward in the bow , along with a deep cycle battery (51lbs) load was solo fat guy (me) 240 # Sophie the gun dog #82 and light load of gear, no decoys or extra person.
 
Phil, in total agreement , as I noted it's not a concern ,just a observation , the feel of the stability is a higher priority then top end speed.The places I go , I ha e plenty of speed , I'm looking for the combination of safety and concleament.
 
Steve,
Same deal with my BB2 with a 25 hp Yamaha. I adjusted the engine up until it started to feel loose on the water, then dropped it down a hair. It then porpoised with 6 gallons under the front deck, so I added small wedges (was actually 3/8 waste from scarfing for the build). This totally fixed the issue with the tank forward, but I now run the tank in the back so that the nose comes up to better handle rough water, and will pick up a little harmonic at WOT with a light load on calm days. A change in throttle or direction will usually make it stop, then it's back to WOT. The boats can be a lot of fun.
Happy Easter.
v/r
Bill
 
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Bill, your description of the harmonics is more accurate ,and yes is was super calm, like a glass mirror when it happened, interesting how the same thing happens , far apart in distance (Pacific Northwest here) . That is what is so helpful on this forum and what a great place to ask questions about, you receive knowledge answers. And yes the boats are a lot of fun, the Lab is in full love with it.
Happy Easter to all today...
 
I don't own one of these boats, but I have a bit of experience with others.


I wonder if a couple small trim tabs, (or maybe that's what Bill Burress is referring to as his "wedges"?), would help. I've seen little hydroplane racing boats with tiny little razor sharp trim tabs that they adjust to water, waves, wind, weight etc. They work wonders.


Just a thought...


Jon
 
Jon, not owning one the the boats ,your spot on for the fix, this one is so small I may not address it, then again, another reason to tinker with the boat, maybe that's the common draw, it's just fun to work on these
 
It will porpoise less with a hunting load. Sounds fine to me. Only thing I'd say to mess with it is IF you have a lot of negative trim on the motor now. If you do, I'd adjust the trim to neutral and then add interceptor plates or wedges until the porpoising went away at that trim.
 
Ted, I agree about with the hunting load it will be reduced further,as it is now its not a big issue, the Mercury has a stainless River Runner that is a prop protector, I will remove that and retest,I think it's creating additional drag and may... Contribute to the hydro effect, I will post the results, thanks for the input.
 
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